Activities for CS1 in Python

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IntroCS

Activities for CS1 in Python

Student Workbook

Tricia Shepherd, Chris Mayﬁeld, Helen Hu

With contributions from Michael Stewart, Theresa Wilson, and Barbara Wahl

Fall 2019

Attribution-NonCommercial-ShareAlike 4.0 International License.

Contents

Introduction to Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Model 1 Getting Started with Thonny

Model 2 Python Built-In Functions

Model 3 Variables and Assignment

Arithmetic Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Model 1 Python Calculator

Model 2 Dividing Numbers

Model 3 Integers and Floats

Basic Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Model 1 Lists

Model 2 Sequences

Model 3 Dictionaries

Conditions and Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Model 1 Comparison Operators

Model 2 / Statements

Model 3 Boolean Operations

Loops and Iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Model 1 Statements

Model 2 The Function

Model 3 Statements

Deﬁning Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Model 1 Flow of Execution

Model 2 Passing Arguments

Model 3 Returning Values

Lists and Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Model 1 Working with Lists

Model 2 Indexing and Slicing

Model 3 Common String Methods

Importing Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Model 1 Random Numbers

Model 2 Multiple Modules

Model 3 Turtle Graphics

Nested Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Model 1 Lists of Lists

Model 2 Nested Loops

Model 3 Nested Dictionaries

File Input/Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Model 1 Writing to a File

Model 2 Appending to a File

Model 3 Reading from a File

Visualizing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Model 1 Simple Plot

Model 2 Histograms

Model 3 CSV Data

Deﬁning Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Model 1 Attributes and Methods

Model 2 Constructors

Model 3 Object-Oriented

Extending Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Model 1 UML Class Diagrams

Model 2 Single-Class Approach

Model 3 Derived Classes

Recursive Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Model 1 Factorial Function

Model 2 Fibonacci Numbers

Model 3 Summation

Role Cards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Meta Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Team Roles, Team Disruptions, What Employers Want, Group vs Team, POGIL Research

Honor Code Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Panic Attack, A Friend Indeed, Oops!, Too Close for Comfort,

Let’s Make a Deal, A Friendly Assist, A Team Effort

Introduction to Python

In this course, you will work in teams of 3–4 students to learn new concepts. This activity will

introduce you to the process. We’ll take a ﬁrst look at variables, assignment, and input/output.

Content Learning Objectives

After completing this activity, students should be able to:

• Describe differences between program and output text.

• Identify and execute Python functions for input/output.

• Write assignment statements and use assigned variables.

Process Skill Goals

During the activity, students should make progress toward:

• Leveraging prior knowledge and experience of other students. (Teamwork)

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Model 1 Getting Started with Thonny

Thonny is an integrated development environment (IDE) for Python designed for learning and

teaching programming. It is freely available at https://thonny.org/.

Do not run Thonny yet! Answer the questions ﬁrst!

Questions (15 min) Start time:

1. Based on the screenshot in Model 1:

a) where is the Shell window?

b) where is the Editor window?

c) what is the name of the ﬁle in the Editor?

d) what is the directory where this ﬁle is located?

2. Identify the number of lines corresponding to:

a) the program (in the Editor)

b) the output of the program

3. What is the symbol at the start of a line of program text not displayed as output?

4. Consider the three program lines (in the Editor) that are not displayed as output. Describe

what might be the purpose of:

a) a comment line (starts with a pound sign: )

b) a blank line

Now open Thonny on your computer, type the code shown in Model 1, save the ﬁle as hello.py, and

run the program. Ask for help if you get stuck!

5. What was required before the third line of the program output was displayed?

6. In the Shell window, what is the color of:

a) the program’s output?

b) the user’s input?

7. Based on your experience so far, what is the difference between the text in the Editor window

and the text in the Shell window?

8. Describe what appears to be the purpose of each line of Python code in the Editor window.

a) line 1:

b) line 2:

c) line 3:

d) line 4:

e) line 5:

f) line 6:

Model 2 Python Built-In Functions

You can use built-in Python functions to perform speciﬁc operations. Sometimes a function

will require information (referred to as arguments) to perform its operation. A function will

also return a result after the operation.

To call (or use) a Python function:

• You must include parentheses after the function’s name (e.g., prints a blank line).

• If the function takes one or more arguments to perform its operation, you must put that

information in the parentheses (e.g., prints a message).

Do not type anything yet! Read the questions ﬁrst!

Python code Shell output

Questions (15 min) Start time:

9. List the names of the three functions used in Model 2.

10. What are the arguments of the ﬁrst use of the function?

11. Type each line of code in a Python Shell, one line at a time, and write the corresponding

output (if observed) in the right column of the table. If an error occurs, write what type of error

it was (i.e., the ﬁrst word of the last line of the error message).

Place an asterisk (*) next to any output for which you were surprised, and note what was unex-

pected about the output. Don’t worry yet about understanding any strange output you may see;

we will discuss what it all means by the end of class.

12. Which function delayed execution until additional input was entered?

13. Which term, user or programmer, best deﬁnes the role of the person who entered the

additional input? Explain.

14. Based on the Shell output, what does the word represent, and how did it get its value?

15. What does the word represent, and how did it get its value?

16. Do the values of and both represent a number? Explain why or why not.

Model 3 Variables and Assignment

In programming, an assignment statement saves a value to a variable. The variable “is set to”

the value after the operator. Selecting concise yet descriptive variable names is considered

good programming style and will make your programs easier to read.

Do not type anything yet! Read the questions ﬁrst!

Python code Shell output

Questions (15 min) Start time:

17. Based on the information and Python code in Model 3, give an example representing each

of the following:

a) an assignment statement

b) the variable being assigned

c) the assignment operator

d) the value of the variable immediately after the assignment

18. Similar to Model 2, type each line of code in a Python Shell and write the corresponding

output in the space above. If an error occurs, write what type of error. Place an asterisk (*) next

to any output for which you were surprised.

19. Circle each successful assignment statement in Model 3. How many are there?

20. What is the observed output of a successful assignment statement?

21. After the successful execution of an assignment statement, how can you conﬁrm the value

of this variable?

22. For each assignment statement that executed without an error, write the corresponding

variable name.

23. Based on the Model 3 output, indicate whether each statement below is true or false.

a) Variable names in Python can start with a number.

b) Variable names in Python must start with a lower-case letter.

c) Variable names in Python may not include spaces.

d) Variable names in Python are case-sensitive.

24. Each of the following assignment statements has an error. Write a valid line of Python code

that corrects the assignment statement. Double-check your code using a computer.

25. Predict the value of the variable after executing all lines of code in Model 3. Then test

your prediction on a computer, and explain the result.

26. Write a line of Python code to assign the current value of to the variable . Show

output that conﬁrms that you have done this correctly, and explain the code.

Arithmetic Expressions

Now that you’ve written a few programs, let’s take a step back and discuss how to do arith-

metic. The behavior of Python operators (+, -, *, /) depends on what type of data you have.

Content Learning Objectives

After completing this activity, students should be able to:

• Execute mathematical expressions similar to a calculator.

• Describe the function of the three Python division operators.

• Explain differences between integer and ﬂoating-point data.

Process Skill Goals

During the activity, students should make progress toward:

• Recognizing mathematical operations based on tables. (Information Processing)

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Model 1 Python Calculator

In a Python Shell window, “ ” is a prompt indicating that the interpreter is waiting for input.

All text entered after the prompt will be executed immediately as Python code.

If you type a Python expression (code that results in a value) after the prompt, Python will

show the value of that expression, similar to a calculator. You can use Python’s module to

perform more complex mathematical operations like logarithms and trigonometric operations.

Do not type anything yet! Read the questions ﬁrst!

Python code Predicted output Actual output

Questions (15 min) Start time:

1. In the middle “Predicted output” column, write what value you expect will be displayed,

based on your team’s experience using a calculator. If there are any lines you are not conﬁdent

about, place an asterisk next to your predicted output.

2. Open a Python Shell on your computer. Type each Python expression at the prompt, one

line at a time, and write the corresponding Python output in the third column above. If an error

occurs, write what type of error it was (i.e., the ﬁrst word of the last line of the error message).

3. What does the ** operator do?

4. Based on the Python code in Model 1, identify four examples of:

a) mathematical operator

b) mathematical function

5. For addition and multiplication to produce an output with a decimal value, what type of

number must be part of the input? Provide justiﬁcation for your team’s answer.

6. Does division follow the same rule as in #5? Provide justiﬁcation for your team’s answer.

7. The output of Model 1 displayed three different errors. Explain the reason for each:

a) TypeError

b) 1st NameError

c) 2nd NameError

8. Identify two differences between using a Python built-in function (e.g., ) and a function

from the module.

Model 2 Dividing Numbers

Table A

evaluates to

2.25

evaluates to

2.5

evaluates to

2.75

evaluates to

3.0

evaluates to

3.25

evaluates to

3.5

evaluates to

3.75

evaluates to

4.0

Table B

evaluates to

Table C

evaluates to

Questions (15 min) Start time:

9. For each operator in Model 2, identify the symbol and describe the type of numerical result.

10. If the result of the / operator were rounded to the nearest integer, would this be the same

as the result of the // operator? Explain how the results in Table A compare to Table B.

11. If the table included more rows, list all numbers // 4 would evaluate to 2 and all the

numbers // 4 would evaluate to 4.

12. Based on the results of Table C, propose another number % 4 evaluates to 0, and explain

what all these numbers have in common.

13. Consider the expressions in Table C that evaluate to 1. How do the left operands in these

expressions (i.e., 9, 13) differ from those that evaluate to 0?

14. Describe the reason for the repeated sequence of numbers (0, 1, 2, 3) for the result of % 4.

15. Recall how you learned to do long division in elementary school. Finish solving for 79 ÷ 5

below. Which part of the answer is , and which part is ?

16. Imagine that you are given candy mints to divide evenly among your team members.

a) If your team receives 11 mints, how many mints would each student get, and how many

are left over? Write a Python expression to compute each result.

b) If your team receives 2 mints, how many mints would each student get, and how many

are left over? Write a Python expression to computes this result.

17. Python has three division operators: “ﬂoor division”, “remainder”, and “true division”.

Which operator (symbol) corresponds to each name?

Model 3 Integers and Floats

Every value in Python has a data type which determines what can be done with the data. Enter

the following code, one line at a time, into a Python Shell. Record the output for each line (if

any) in the second column.

Python code Shell output

Questions (15 min) Start time:

18. What is the data type ( , , or ) of the following values? (Note: if you’re unsure,

use the function in a Python Shell.)

a) pi

b) integer

c) word

d) number

19. List the function calls that convert a value to a new data type.

20. How does the behavior of the operators (+ and *) depend on the data type?

21. What is the difference between the function and the function?

22. What is the value of ? What is the value of ? If you enter these

expressions into a Python Shell, what do you notice about the results?

23. In order to store a number with 100% accuracy, what data type is required? How might

you precisely represent a bank account balance of $123.45?

24. Try calculating a very large integer in a Python Shell, for example, 123

456

. Is there a limit to

the integers that Python can handle?

25. Try calculating a very large ﬂoating-point number in a Python Shell, for example, 123.0

465

Is there a limit to the ﬂoating-point numbers that Python can handle?

26. Summarize the difference between the numeric data types ( and ). What are their

pros and cons?

Basic Data Structures

Python has a wide variety of built-in types for storing anything from numbers and text (e.g.,

, , ) to common data structures (e.g., , , ).

Content Learning Objectives

After completing this activity, students should be able to:

• Reference a speciﬁc element of a sequence by an index.

• Compare and contrast numeric and sequence data types.

• Create a dictionary of strings and look up values by key.

Process Skill Goals

During the activity, students should make progress toward:

• Providing feedback on how well other team members are working. (Teamwork)

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Model 1 Lists

A variable can hold multiple values in the form of a list. The values are separated by commas

and wrapped in square brackets. For example:

Each element of the list can be referenced by an index, which is the sequential position starting

at 0. For example, is 11.

index 0 1 2 3 4 5 6 7 8 9

value 2 3 5 7 11 13 17 19 23 29

Do not type anything yet! Read the questions ﬁrst!

Python code Shell output

Questions (10 min) Start time:

1. What is the index of the second element of ? What is the value at that index?

2. How does the index number compare to the position of the element?

3. Type each line of code in a Python Shell and write the corresponding output in the space

above. If an error occurs, write what type of error. Place an asterisk (*) next to any output for

which you were surprised.

4. How did you reference the value of the 3rd element of ?

5. What did the output of the len() function tell you about the list?

6. The output of Model 1 displayed an error. Explain the reason for the error.

7. Write a statement that assigns a list of three integers to the variable .

8. Write a statement that assigns the value 100 to the last element of .

9. Write a statement that assigns the ﬁrst value of to a variable named .

Model 2 Sequences

Lists and strings are examples of sequence types. Complete the table below to explore how

sequences work.

Python code Shell output

Questions (15 min) Start time:

10. How does a sequence type differ from a number? (See the last row of the table.)

11. What are the names of the three sequence types introduced in Model 2?

12. How does the syntax of creating a tuple differ from creating a list?

13. Is there more than one way (syntax) to create a tuple? Justify your answer.

14. Which sequence types allow their elements to be changed? Which do not?

15. Is it possible to store values of different types in a sequence? If yes, give an example from

the table; if no, explain why not.

16. Summarize the difference between lists and tuples. How do they look differently, and how

do they work differently?

Model 3 Dictionaries

In Python, a dictionary stores “ ” pairs. The pairs are separated by commas and

wrapped in curly braces. For example:

Key Value

In contrast to sequence types, a dictionary is a mapping type. Values are referenced by keys,

rather than by indexes.

Type the dictionary above into a Python Shell, and then complete the following table

to explore how it works.

Python code Shell output

Questions (20 min) Start time:

17. List all the keys stored in the dictionary after completing the table.

18. What is the data type of the keys in the dictionary?

19. Explain the reason for the error after entering each of the following lines:

20. Ignoring the ”dict_items()” part, describe the contents and type of data returned by the

method.

21. Write a Python expression that creates a dictionary for the seven days of the week, i.e.,

Sun=1, Mon=2, Tue=3, etc. Assign the dictionary to the variable .

22. If you assign two different values to the same key (i.e., two assignment statements with

one value each), which value is stored in the dictionary? Justify your answer with an example.

23. Another way to store the data in Model 3 is to use two lists:

What is a disadvantage of this approach? Explain your reasoning.

Conditions and Logic

Computer programs make decisions based on logic: if some condition applies, do something,

otherwise, do something else.

Content Learning Objectives

After completing this activity, students should be able to:

• Evaluate boolean expressions with comparison operators (<, >, <=, >=, ==, !=).

• Explain the syntax and meaning of / statements and indented blocks.

• Evaluate boolean expressions that involve comparisons with , , and .

Process Skill Goals

During the activity, students should make progress toward:

• Evaluating complex logic expressions based on operator precedence. (Critical Thinking)

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Model 1 Comparison Operators

In Python, a comparison (e.g., ) will yield a Boolean value of either or .

Most data types (including , , , , and ) can be compared using the fol-

lowing operators:

Operator Meaning

less than

less than or equal

greater than

greater than or equal

equal

not equal

Type the following code, one line at a time, into a Python Shell. Record the output for each line

(if any) in the second column.

Python code Shell output

Questions (10 min) Start time:

1. What is the name of the data type for Boolean values?

2. Do the words and need to be capitalized? Explain how you know.

3. For each of the following terms, identify examples from the table in Model 1:

a) Boolean variables:

b) Boolean operators:

c) Boolean expressions:

4. Explain why the same expression had two different results.

5. What is the difference between the operator and the operator?

6. Write a Boolean expression that uses the operator and evaluates to .

Model 2 / Statements

An statement makes it possible to control what code will be executed in a program, based

on a condition. For example:

Python uses indentation to deﬁne the structure of programs.

The line indented under the statement is executed only when

is . Likewise, the line indented under the

statement is executed only when is . The

ﬂowchart on the right illustrates this behavior.

Questions (15 min) Start time:

7. What is the Boolean expression in Model 2?

8. Enter this short program into a Python Editor. What is the output when the user enters the

number 5? What is the output when the user enters the number -5?

9. After an if-condition, what syntax differentiates between (1) statements that are executed

based on the condition and (2) statements that are always executed?

10. Enter the line into a Python Editor (where is a space), save the ﬁle

as , and run the program. What happens if you indent code inconsistently?

11. Based on the program in Model 2, what must each line preceding an indented block of code

end with?

12. Write an statement that ﬁrst determines whether is even or odd, and then prints

the message or . (Hint: use the operator.)

13. Does an statement always need to be followed by an statement? Why or why not?

Give an example.

Model 3 Boolean Operations

Expressions may include Boolean operators to implement basic logic. If all three operators

appear in the same expression, Python will evaluate ﬁrst, then , and ﬁnally . If there

are multiple of the same operator, they are evaluated from left to right.

Do not type anything yet! Read the questions ﬁrst!

Python code Predicted output Actual output

Questions (20 min) Start time:

14. What data type is the result of ? What data type is the result of ?

15. Predict the output of each print statement, based on the variables , , and .

Then execute each line in a Python Shell to check your work.

16. Based on the variables in #15, what is the value of a < b? What is the value of b < c?

17. If two Boolean expressions are compared using the operator, what is the resulting

Boolean value?

18. Using the variables deﬁned in #15, write an expression that will compare two Boolean

expressions using the operator. Check your work using a Python Shell.

19. Assuming and each represent a Boolean expression that evaluates to the Boolean value

indicated, complete the following table. Compare your team’s answers with another team’s,

and resolve any inconsistencies.

False False

False True

True False

True True

20. Assume that two Boolean expressions are compared using the operator. If the value

of the ﬁrst expression is , is it necessary to determine the value of the second expression?

Explain why or why not.

21. Assume that two Boolean expressions are compared using the operator. If the value

of the ﬁrst expression is , is it necessary to determine the value of the second expression?

Explain why or why not.

22. Examine the last row of the table in #15. Evaluate the Boolean expression following the

order of precedence rules explained in Model 3. Show your work by rewriting the line at each

step and replacing portions with either or .

23. Suppose you wanted to execute the statement only when both and are

positive. Determine the appropriate operators, and write a single Boolean expression for the

if-condition.

24. Rewrite the expression from #23 using the operator. Your answer should yield the same

result as in #23, not the opposite. Describe in words what the new expression means.

25. Suppose that your team needs to execute the statement except when both

and are positive. Write a Boolean expression for this condition. How is it different from the

previous question?

Loops and Iteration

A loop allows you to execute the same statements multiple times. Python has two kinds of

loop structures: loops, which iterate over the items of a sequence, and loops, which

continue to execute as long as a condition is true.

Content Learning Objectives

After completing this activity, students should be able to:

• Explain the syntax and the purpose of a statement.

• Predict how works given 1, 2, or 3 arguments.

• Identify the three main components of a loop.

Process Skill Goals

During the activity, students should make progress toward:

• Tracing the execution of while/for loops and predict their ﬁnal output. (Critical Thinking)

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Model 1 Statements

A loop executes the same block of code “for each item in a sequence”. Create a new ﬁle

named , and enter the following code:

Questions (15 min) Start time:

1. Run the program. How many times does the indented line of code execute under

the loop?

2. How many times does the line of code NOT indented execute after the loop?

3. Identify the value of each time the indented line of code is executed.

a) 1st time:

b) 2nd time:

c) 3rd time:

4. Modify the list in the following ways, and rerun the program each time. Indicate

how many times the loop executes.

a) non-consecutive numbers:

b) numbers decreasing in value:

c) all have the same value:

d) single value in a list:

5. In general, what determines the number of times that the loop repeats?

6. What determines the value of the variable ? Explain your answer in terms of what is

assigned ( ) each time the loop runs.

7. Modify the program as follows:

a) Write a statement that assigns to the variable .

b) Rewrite the statement to use the variable instead.

c) Does the assignment need to come before or after the statement?

8. Add the following code at the end of your program:

a) What is the output of this statement?

b) What determined how many times was called?

c) Explain what a statement does with strings.

9. What other data types (besides lists and strings) can a loop handle? Experiment by

adding examples to your program. Summarize here what works and what doesn’t.

Model 2 The Function

The Python function will generate a list of numbers. The function can take up to

three numbers as arguments. Fill in the table below by typing the code into a Python Shell:

Python code Shell output

Questions (15 min) Start time:

10. Explain the difference in output between the ﬁrst two lines of code (with and without the

function).

11. If the argument of the function speciﬁes a single number (x):

a) What will be the ﬁrst number listed?

b) What will be the last number listed?

c) How many numbers will be in the list?

d) Use the range function to generate the sequence 0, 1, 2, 3.

12. If the argument of the function speciﬁes two numbers (x, y):

a) What will be the ﬁrst number listed?

b) What will be the last number listed?

c) How many numbers will be in the list?

d) Use the range function to generate the sequence 1, 2, 3, 4.

13. If the argument of the function speciﬁes three numbers (x, y, z):

a) What will be the ﬁrst number listed?

b) What does the third argument represent?

c) How many numbers will be in the list?

d) Use the range function to generate the sequence 1, 3, 5, 7.

14. In your Editor, make a copy of the Model 1 code. Then modify the statement so that

the number of times the loop executes is determined by a variable named .

a) How did you change the statement?

b) How would you cause the loop to print the values 0 to 5?

15. Consider the two different types of statements used in Model 1 and Model 2.

a) If you wanted to execute a loop 100 times, which type of statement would you choose

and why?

b) If you wanted to use each item of an existing list inside the loop, which type of state-

ment would you choose and why?

16. Does the function work with strings? If so, show an example. If not, show how to

print the letters A to Z in a loop.

Model 3 Statements

A more general looping structure is the statement. Add the code below to your current

program:

Questions (15 min) Start time:

17. What must the value of the Boolean expression (after the ) be in order for the ﬁrst

print statement to execute?

18. Circle the statement that changes the variable in the above code.

19. What happens to the value of the variable during the execution of the loop?

20. Explain why the loop body does not execute again after it outputs “the number is 2”.

21. Reverse the order of the statements in the loop body:

a) How does the order impact the output displayed by the function?

b) Does the order impact the total number of lines that are output?

22. Identify three different ways to modify the code so that the loop only executes twice.

23. Describe the three parts of a loop that control the number of times the loop executes.

24. Comment out the statement , and run the module. Then press Ctrl-C (hold down

the Ctrl key and press C). Describe the behavior you see, and explain why it happened.

When writing a loop, it’s helpful to answer a few questions before you start:

•

What needs to be initialized before the loop?

•

What condition must be true for the loop to repeat?

•

What will change so that the loop eventually ends?

25. Consider the function that prompts the user for n numbers and returns the sum of

these values. For example, when is called, the user is asked to input ﬁve numbers. If

the user inputs 3, 1, 5, 2, and 4, the function would return the value 15.

a) Describe the variable that needs to be initialized before the loop begins.

b) Describe the Boolean expression that must be true for the loop to continue.

c) Describe what will need to change so that the loop will eventually end.

d) Now list what else needs to happen inside the body of the loop for you to calculate the

sum of the user input.

e) Given your previous answer, are there any other values that need to be initialized before

the start of the loop?

Deﬁning Functions

Python programs typically have one or more functions, each of which has one or more state-

ments. Deﬁning new functions allows you to break down a complex program into smaller

blocks of reusable code.

Content Learning Objectives

After completing this activity, students should be able to:

• Explain the ﬂow of execution from one function to another.

• Describe the syntax of function deﬁnitions and function calls.

• Write short functions that have parameters and return results.

Process Skill Goals

During the activity, students should make progress toward:

• Tracing the execution of functions with Python Tutor. (Information Processing)

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Model 1 Flow of Execution

In addition to using Python’s built-in functions (e.g., , ) and functions deﬁned in other

modules (e.g., ), you can write your own functions.

Questions (20 min) Start time:

1. Based on the program in Model 1:

a) What is the Python keyword for deﬁning a function?

b) On what line is the function deﬁned? called?

c) On what line is the function deﬁned? called?

2. Open a web browser and go to PythonTutor.com. Click on “Visualize your code”, and type

(or paste) the program above. Make sure the line numbers match.

3. Click the “Visualize Execution” button. As you step through the program, pay attention to

what is happening on the left side of the visualization.

a) What does the red arrow indicate?

b) What does the green arrow indicate?

4. Notice the order in which the program runs:

a) After line 12 of the program executes (Step 3), what is the next line that executes?

b) After line 9 of the program executes (Step 6), what is the next line that executes?

5. Go back to the beginning of the program execution. This time as you step through the

program, pay attention to what changes on the right side of the visualization.

a) Describe what changes in the visualization after Step 1.

b) Describe what changes in the visualization after Step 2.

6. In general, what happens on the right side of the visualization when a function is called?

7. In terms of execution order, what is the effect of calling a function?

8. Draw the right side of the visualization for Step 11 in the space below.

9. Notice that the variable is printed from within the function. What happens if

you try to inside the main function?

10. Explain what happened in the previous question in terms of frames in the visualization.

11. In the space below, write a deﬁnition for a function called that prompts the

user to enter a word. The function should convert the string to a list and print the list.

12. Edit the program in Python Tutor so that, instead of deﬁning and calling the function

, it deﬁnes and calls the function . Verify your changes by visualizing

the execution, and draw a picture of the right side immediately after the list is printed.

Model 2 Passing Arguments

Instead of using inside a function to get data, we can deﬁne a function to take a parameter

(variable). When we call the function, we need to provide an argument (value). Change the

program in Python Tutor as follows:

Questions (15 min) Start time:

13. Underline the parameter in the function deﬁnition, then circle each use of the

parameter inside the function.

14. Find the function call in , and underline the argument being passed by the

function call.

15. Visualize the execution of until Step 8.

a) How does the frame for at this point in the execution differ from the frame for

previously?

b) Write the implied assignment statement to show how the parameter gets its value.

c) When a variable is used as an argument, does the name of the variable need to be the

same as the parameter variable name?

16. Assume that and . In the function call :

a) What is the argument for the function call?

b) Write the implied assignment statement that happens during the call.

c) What will be the value of parameter when begins executing?

d) Predict the output that will be produced by the function call.

17. Review the two implied assignment statements that you have written. What exactly gets

“passed” when you call a function?

18. Change so that, instead of multiplying by the length of , it will mul-

tiply by an integer passed as the second argument to the function. Write the new version of

in the space below. Use for the name of the new integer parameter.

19. How does the call to in need to change so that it matches the new function

deﬁnition? Give an example.

Model 3 Returning Values

Functions may optionally send a value back to the calling function using a statement.

Change the program in Python Tutor as follows:

Questions (10 min) Start time:

20. Aside from the function name, how does line 8 in Model 3 differ from line 8 in Model 2?

21. At what step number (in the simulation) has completed its execution, but

control has not yet returned to the function?

In the space below, draw the frame for after this step.

22. In general, what value will be returned by ?

23. What changes in the frame for at Step 12 of the execution?

24. Edit and delete the return statement at the end of the function. Visualize the

execution. What value is returned by a function when there is no return statement?

25. Edit again, and add the return statement back to the end of the function. Then

change line 8 so that is still called but there is no assignment to . What do

you predict will happen in after the function call completes?

26. Why is a function that returns the value of a variable more useful than a function that

simply prints the value of that variable?

Lists and Strings

Many interesting problems involve manipulating sequences of data. You’ve learned about lists

and strings before, but this activity provides a more in-depth look at what they can do.

Content Learning Objectives

After completing this activity, students should be able to:

• Name four methods that lists provide, and describe what each method does.

• Explain the syntax and meaning of slice operations, with and without indexes.

• Name four methods that strings provide, and describe what each method does.

Process Skill Goals

During the activity, students should make progress toward:

• Gaining insight about data structures from many examples. (Information Processing)

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Model 1 Working with Lists

Recall that a variable can hold multiple values in the form of a list. The values are separated by

commas and wrapped in square brackets.

Lists have methods (built-in functions) that can be called using dot notation. For example, to

add a new element to the end of a list, we can use the method.

Python code Shell output

Questions (15 min) Start time:

1. What is the result of calling the method on a list?

2. What must be deﬁned prior to using a method like ?

3. Explain why two lines in Model 1 caused an .

4. What is the result of calling the method on a list?

5. Based on the output, name several list methods not shown in Model 1. Do not include

methods that begin and end with two underscores (e.g., __add__).

6. Give one example of a list method that requires an argument and one that does not.

7. Describe the similarities and differences between using a list method like and Python

built-in functions like .

8. Complete the function below (two lines are missing). It should prompt the user for numbers

and build a list by adding one number at a time to the end of the list. The loop terminates when

the user inputs the number 0.

Model 2 Indexing and Slicing

A string is a sequence of characters in single quotes ( ) or double quotes ( ). Depending on

the application, we can treat a string as a single value (e.g., ), or we can access individual

characters using square brackets (e.g., ). We can also use slice notation (e.g., )

to refer to a range of characters. In fact, all types of sequences (including and )

support indexing and slicing.

Python code Shell output

Questions (15 min) Start time:

9. What is the positive index of each character in the string? Check your answers above.

Character: C T G A C G A C T T

Index:

10. What is the negative index of each character in the string? Check your answers above.

Character: C T G A C G A C T T

Index:

11. Based on the previous questions, what are and ? Explain your answers.

12. Explain the IndexError you observed. What is the range of indexes for the string?

13. Consider the notation of the operator for slicing the string.

a) Is the value at the same as the corresponding index value (i.e., )? If not, describe

what it means.

b) Is the value at the same as the corresponding index value (i.e., )? If not, describe

what it means.

c) Explain what it means when only a single number is referenced when creating a slice, such

as or .

14. What is the simplest way to get the ﬁrst three characters of ? What is the simplest way

to get the last three characters?

15. Write a Python expression that slices from using positive indexes. Then write

another expression that slices the same string using negative indexes.

16. Write a Python assignment statement that uses the function to assign the last letter of

to the variable .

17. Write a Python assignment statement that uses a negative index to assign the last letter of

to the variable .

Model 3 Common String Methods

Like lists, strings have methods (built-in functions) that can be called using dot notation. See

https://docs.python.org/3/library/stdtypes.html#string-methods for more details.

Python code Shell output

Questions (15 min) Start time:

18. Does the method change the contents of the string? Justify your answer.

19. Describe the function—what does return in Model 3?

20. Why is it possible to call the method on but not ?

21. Name several other string methods not shown in Model 3. (Read the documentation.)

22. Consider the application of a method on a variable:

a) Does a string variable change after applying a method? Provide justiﬁcation.

b) Does a list variable change after applying a method? Provide justiﬁcation.

c) Identify the data type that is immutable (i.e., the value never changes).

23. Write a single statement to change the ﬁnal contents of to .

Conﬁrm that your code works in a Python Shell.

24. Why do you think Python has a method for strings but not for lists?

Importing Modules

Python comes with an extensive library of built-in modules that make it easy to accomplish

everyday tasks. With just a few lines of code, you can do anything from generating random

numbers and drawing graphics to sending emails and accessing websites.

Content Learning Objectives

After completing this activity, students should be able to:

• Use the module to generate random ﬂoat and integer sequences.

• Explain the purpose of the common line .

• Summarize several built-in modules, including and .

Process Skill Goals

During the activity, students should make progress toward:

• Navigating the Python standard library documentation. (Information Processing)

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Model 1 Random Numbers

You can generate a sequence of numbers using the Python module. A mathematical

function is used to produce the sequence based on a seed value. (If no seed is given, the current

system time is used.) The sequence is more accurately described as pseudorandom, since its

output is inherently predictable.

Python code Shell output

Questions (20 min) Start time:

1. What is the name of the module that must be imported before generating a random number?

2. Based on Model 1, what are the names of three functions deﬁned in the module?

3. Identify the syntax of the statement to import:

a) a module

b) a function

4. Identify the syntax of a function call assuming:

a) the module was imported

b) the function was imported

5. How could you eliminate the need for typing the word “random” twice (in a function call)

to generate a random number?

6. Compare the shell output of your team with at least one other team. Describe the similarities

and differences observed.

7. What is the effect on the random numbers generated after calling the method?

8. Describe one reason to set the same seed each time a program is run, and one reason to not

use the method.

9. Run multiple times. Based on the results, describe:

a) the range of numbers returned by the function

b) the nature of the distribution of numbers generated. (Do they appear clustered around a

particular value, or are they spread out uniformly over the range?)

10. Run multiple times. Based on the results, describe:

a) the range of numbers returned by the function

b) the nature of the distribution of numbers generated. (Do they appear clustered around a

particular value, or are they spread out uniformly over the range?)

Model 2 Multiple Modules

Create a new ﬁle , and enter the code:

Run , and record the output below.

Create a new ﬁle (in the same directory), and enter the code:

Run , and record the output below. Draw an arrow from each line of output to its

corresponding print statement in the code.

Questions (15 min) Start time:

11. Upon execution of :

a) what is the value of the variable ?

b) does the output correspond solely to the print statements contained in this ﬁle?

12. Upon execution of :

a) what is the value of the variable from the print statement in

b) what is the value of the variable from the print statement in

c) does the output correspond solely to the print statements contained in this ﬁle?

13. What was the reason to include the statement in ?

14. Based on the output of , describe what happens (as a side effect) when another

module is imported.

15. What line in did not print when was executed? Why?

16. In order for the output of to correspond solely to the print statements contained in

, what modiﬁcations need to be made to ?

17. Describe what code in general to include inside , and why.

Model 3 Turtle Graphics

The module can be used to create graphics. Create a new ﬁle (in the same

directory), and enter the following code. Run the program and see what happens.

Questions (10 min) Start time:

18. For each outcome, describe the type of edit necessary to and :

a) a blue turtle

b) a longer simulation

c) a smaller range of angles (e.g., -45 to 45) that deﬁne the direction of the turtle

d) a random range of integers (e.g., 10 to 20) that deﬁne the length of a turtle move

19. Describe the type of edit necessary to produce the same outcome in Question #18d if the

argument of is instead of 10:

20. Go to https://docs.python.org and click the link in the upper right corner. Find at

least two built-in modules that interest you, and summarize what functions they provide.

Nested Structures

Containers are objects that store other objects. For example, stores a sequence of objects,

and stores a mapping of objects to objects. Containers can also hold other containers,

which makes it possible to represent any type (or shape) of data.

Content Learning Objectives

After completing this activity, students should be able to:

• Explain how rows and columns of data can be stored in lists.

• Write nested for loops to iterate data and compute functions.

• Navigate a complex data structure with dictionaries and lists.

Process Skill Goals

During the activity, students should make progress toward:

• Developing algorithms that loop through lists to compute a result. (Problem Solving)

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Model 1 Lists of Lists

Connect Four (® Hasbro, Inc.) is a two-player game in which the players take turns dropping

colored discs into a six-row by seven-column grid. The objective of the game is to be the ﬁrst

player to form a horizontal, vertical, or diagonal line of four of one’s own discs. (paraphrased

from https://en.wikipedia.org/wiki/Connect_Four)

Enter the code above into a Python Shell, and run each line of the table below. If the output

is longer than one line, summarize it with a few words.

Python code Shell output

Questions (15 min) Start time:

1. What does look like when you ﬁrst it? (How is the output different from the

original format shown in Model 1?)

2. What does look like when you use instead? Explain what means.

3. When viewed as a rectangle, how many “rows” and “columns” does have?

4. What type of object is ? What type of objects does it contain?

5. What type of object is ? What type of objects does it contain?

6. In the expression , which index corresponds to the row, and which index corre-

sponds to the column?

7. Is a list of rows or a list of columns? Justify your answer.

8. Describe how to append one more row to .

9. What is necessary to append a “column” to ?

Model 2 Nested Loops

Example A

We typically use a loop to examine the contents of a list:

Example B

If a list contains another list, we need a loop that contains another loop. For example,

to count the “spaces” in the from Model 1:

Questions (15 min) Start time:

10. As a team, discuss the two examples from Model 2. Predict how many times each of the

following lines will execute. Then run the code and check your answers based on the output.

a) How many times does Line 3 execute? Predicted: Actual:

b) How many times does Line 6 execute? Predicted: Actual:

c) How many times does Line 8 execute? Predicted: Actual:

d) How many times does Line 10 execute? Predicted: Actual:

11. What determined how many times the “ ” loop would run?

12. Answer the following questions in terms of .

a) What determined how many times the “ ” loop would run?

b) What determined how many times the “ ” loop would run?

13. In the example below, predict how many times the statement will execute. Then run

the code to verify your answer.

14. Rewrite the nested loops in Model 2 Lines 4–10 using the function. Replace

the variables and with and , respectively. For simplicity, you may omit the

statements in your answer.

15. Write a loop (using ) that computes the factorial of a given integer n. Recall that

n! = n ∗ (n − 1) ∗ (n − 2) ∗ . . . ∗ 1. Store your result in a variable named .

16. Write nested loops that compute and display the factorial of each integer from 1 to 20. Use

your code from the previous question as the inner loop. Your output should be in this format:

Model 3 Nested Dictionaries

Containers can be nested in arbitrary ways. For example, the following data could be described

as a “dictionary of dictionaries of integers and lists of strings”.

Enter the following code into a Python Shell, and complete the table. If the output is longer

than one line, summarize it with a few words.

Python code Shell output

Questions (15 min) Start time:

17. Explain the you encountered.

18. In the expression , describe the purpose of the strings

and .

19. When iterating a dictionary using a loop (i.e., ), what gets assigned to

the variable?

20. What is wrong with the following code that attempts to each movie?

21. Write nested loops that output every genre found under the dictionary. You should

have nine total lines of output.

22. Each movie in Model 3 has a title, a year, and three genres.

a) Is it necessary that all movies have the same format?

b) Name one advantage of storing data in the same format:

c) Show how you would represent The LEGO Movie (2014) with a runtime of 100 min and

the plot keywords “construction worker” and “good cop bad cop”.

File Input/Output

Most data is stored in ﬁles, not input by the user every time. In this activity, you’ll learn the

basics of reading and writing plain text ﬁles.

Content Learning Objectives

After completing this activity, students should be able to:

• Create a new text ﬁle, and output several lines to it.

• Open an existing ﬁle, and append several lines to it.

• Read a text ﬁle line by line, and extract data from it.

Process Skill Goals

During the activity, students should make progress toward:

• Justifying answers based on the results of an experiment. (Critical Thinking)

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Model 1 Writing to a File

The following example creates a new ﬁle (in the current/default folder) named and

writes several lines of output to it. Run the code, and examine the contents of the resulting

ﬁle. In the space below, write the contents of to the right of the code.

Questions (15 min) Start time:

1. Based on the Python code:

a) How many arguments are passed to ? What are their types?

b) What variable stores the ﬁle object returned by the function?

c) Identify the names of all methods used on this ﬁle object in the code.

d) What type of data does the method require for its argument?

2. Based on the ﬁle:

a) How many times was the method called to create the ﬁrst line of text?

b) How many times was the write method called to create the second line of text?

c) What does the character do?

d) How is the method different from the function?

3. Write a program that creates a ﬁle named and writes 100 lines like this:

Model 2 Appending to a File

The second argument of speciﬁes the mode in which the ﬁle is opened. When writing

output to a ﬁle, there are two basic modes:

• The write ( ) mode will overwrite/replace the ﬁle contents.

• The append ( ) mode will add new data to the end of the ﬁle.

Either mode will create the ﬁle automatically if it does not already exist. Enter the following

lines into a Python Shell, and record the output at each step.

Python code Shell output

Questions (10 min) Start time:

4. Explain what happens as a result of the line:

5. How do the arguments passed to the function differ for writing a new ﬁle in comparison

to appending an existing ﬁle?

6. What does the method return? Run to check your answer.

7. Explain the reason for the error observed after entering:

a) the ﬁrst line of code:

b) the last line of code:

c) the statement:

Model 3 Reading from a File

Programs often require input data from an external ﬁle source. Not surprisingly, there are

methods for reading the contents of ﬁles. Enter the following lines into a Python Shell.

Python code Shell output

Questions (20 min) Start time:

8. Based on the output above:

a) What type of data does the method return?

b) What type of data does the method return?

9. Why did the method return different values each time?

10. What happens if you try to read past the end of the ﬁle? Justify your answer.

11. What is the difference between the two loops in Model 3?

12. Consider the output of the ﬁrst loop:

a) Why does the program display the ﬁle as if it were double spaced?

b) How would you change the code to avoid printing extra blank lines?

13. Based on the second half of Model 3:

a) Why was it necessary to open the ﬁle again?

b) Write code that would output 1.0 using

c) Write code that would output 1.0 using

14. Consider a ﬁle that contains ﬁrst and last names of 100 people, with one name

per line (e.g., “Anita Borg”). Write a program that prints all the last names (the second word of

each line) in the ﬁle.

Visualizing Data

As a general-purpose programming language, Python is incredibly useful for analyzing data

and visualizing results. This activity is a ﬁrst look at , one of the most widely used

2D plotting libraries.

Content Learning Objectives

After completing this activity, students should be able to:

• Explain the basic structure of code for plotting a mathematical function.

• Analyze visually the behavior of the Python random number generator.

• Read data from a CSV ﬁle and generate histograms of various columns.

Process Skill Goals

During the activity, students should make progress toward:

• Navigating the documentation for a third-party library. (Information Processing)

Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Model 1 Simple Plot

When analyzing data, it’s helpful to create charts, plots, and other visualizations. Doing so

allows you to see important numerical relationships. Enter the following code into a Python

Editor, and run the program.

Questions (15 min) Start time:

1. Identify in the source code which line numbers:

a) generated the data?

b) set the axes properties?

c) displayed the window?

d) plotted the actual data?

2. Describe in your own words what is being plotted.

3. Modify the code to plot only one cycle of the sine wave (instead of two). Write the edited

line of code below.

4. Change the third argument of from 0.01 to 0.15. What is the result?

5. Add as a third argument to the function. What is the result?

6. How does the third parameter of affect how the plot looks?

7. How would you modify the code to plot the function y = x

− 1 instead? Show the results

from -2 to +2.

8. Which three Python libraries are used in Model 1? Quickly search the Internet and ﬁnd their

websites. Write a one-sentence description about each library.

Model 2 Histograms

Recall that you can generate a sequence of numbers using the module. Merge the code

below into your program from Model 1. Run the program, and view the output.

Questions (10 min) Start time:

9. Based on the Python code:

a) What is the range of values generated by the function?

b) How many random values are generated?

10. Based on the ﬁgure plotted:

a) How many bars are displayed?

b) What is the width of each bar?

c) What is the sum of the heights of the bars?

11. Based on your answers above, what are appropriate labels for the x and y axes?

12. Increase the argument of to 1000, 10000, and 100000. Describe how the output

plot changes when you run the program.

13. Add the number 50 as second argument to the function. What is the meaning of the

result?

14. In general, describe what the function does with the list of random numbers to create

this type of plot.

Model 3 CSV Data

“Comma Separated Values” is a common ﬁle format when exporting data from spreadsheets

and databases. Each line of the ﬁle is a row, and each column is separated by a comma. Cells

that contain commas are wrapped in quote marks.

ﬁle contents:

Python includes a module (https://docs.python.org/3/library/csv.html) that makes it easy

to read and write CSV ﬁles.

Program output:

Questions (20 min) Start time:

15. In the example ﬁle above:

a) In what way is the ﬁrst line different?

b) How many rows of data are there?

c) How many columns are there?

16. Compare with the program output:

a) Are quote marks included in the lines of data?

b) Are quote marks included in the program output?

c) What is the purpose of the quote marks?

17. In the Python code above:

a) Which line of code reads the ﬁrst line of the ﬁle?

b) What type of data does the variable contain?

In 2013, the U.S. Department of Education released the “College Scorecard” website to help students

and families compare institutions of higher education. The Scorecard data includes information like

average cost of attendance, graduation and retention rates, student body demographics, etc.

18. Download the “Scorecard Data 7 MB CSV” from https://collegescorecard.ed.gov/data/

(listed halfway down under “Featured Downloads”). Open the CSV ﬁle in Excel or a similar

program, and skim its contents.

a) How many rows does it have?

b) How many columns does it have?

19. Column CH is named UGDS, which means “Enrollment of undergraduate certiﬁcate /

degree-seeking students”.

a) What is the range of values in this column?

b) Which school has the most students enrolled?

c) Do all rows have an integer value for UGDS?

20. Based on the code in Model 2 and Model 3, write a program that plots a histogram of the

UGDS column. Complete the following steps to consider each part of the program.

a) What two import statements will you need at the top?

b) What three statements prepare the csv ﬁle for reading?

c) What code is necessary to read the entire column into a list? (Note: Column CH in Excel

is in Python.)

d) By default, data from text/csv ﬁles are read as strings. Write the code to convert the

values to integers. Be sure not include the values in the ﬁnal list.

e) Write the last two lines that plot and show the histogram.

21. Run the program, and compare your results with another team’s. What does the histogram

tell you about undergraduate enrollments in the United States?

22. What other questions could you ask about this data? How would you answer them using

histograms, line charts, and scatter plots?

Deﬁning Classes

In this activity, we’ll take a ﬁrst look at object-oriented programming. Classes provide a means

of bundling data and functionality together.

Content Learning Objectives

After completing this activity, students should be able to:

• Write a class deﬁnition that has several attributes and methods.

• Explain what a constructor is, when it is called, and what it does.

• Discuss what “object-oriented” means using concrete examples.

Process Skill Goals

During the activity, students should make progress toward:

• Developing and testing the design of a program incrementally. (Problem Solving)

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Model 1 Attributes and Methods

Previously you have used built-in types like , , and . Each of these types comes with

its own methods, such as and . You can create new types of data, and methods

to go with them, by deﬁning a . Classes specify the attributes (instance variables) and

methods (functions) that each object belonging to the class will have.

Questions (15 min) Start time:

1. Examine the class deﬁnition (the top half of the code):

a) What is the name of the class?

b) What are the names of the two methods?

c) What is the name of the ﬁrst parameter for all methods?

2. Now examine the block of code:

a) How many different objects were created?

b) Identify the variable name of each object.

c) How many attributes were assigned in the object? List the names.

d) How do the number of arguments for each method call differ from the number of param-

eters speciﬁed in the method deﬁnition?

3. How does the syntax referencing an attribute differ inside vs. outside the class deﬁnition?

4. When the method is called (in the last two lines), what is the value of the

parameter?

5. Enter the expression in a Python Shell. Explain the meaning and signiﬁcance

of the output.

6. Write code to create a new object called , and assign one of the attributes listed

in Question #2c.

7. Call the method on carbon in a Python Shell. What is the reason for the error?

Model 2 Constructors

For each class deﬁned, you can provide a constructor that initializes attributes of a new object.

In Python, the constructor is always named (with two underscores before and after

the word ). The constructor is called automatically when you create a new object.

Add the following constructor to the top of your class. By convention, the constructor is

typically the ﬁrst method in a class deﬁnition. Also edit the block of code as shown.

... previous methods from Model 1 ...

Questions (15 min) Start time:

8. What is always the name of the constructor?

9. Although there is no direct call to the constructor, explain how you know this method is

executed when an object is created.

10. Consider your answer to Question #7. What is one advantage of deﬁning a constructor for

a class?

11. In a Python Shell, try to create a new object called with only two arguments.

Write your statement in the space below. What is the reason for the error you see?

12. When creating an object of the class, what is the value of if:

a) three arguments are given?

b) four arguments are given?

13. Print the value of in a Python shell.

a) What is the reason for the error?

b) In order to eliminate this error, what should be printed instead?

14. For each line below, what is the value of ?

a) oxygen = Atom(’O’, 8, 15.999, 16)

b) carbon = Atom(’C’, 6, 12.001)

c) oxygen.neutrons()

d) carbon.neutrons()

15. Recall that a variable may be “local” (deﬁned within a function), “global” (deﬁned in the

non-indented or block of code), or “built-in” (part of Python itself).

a) Explain why the attribute is not a global variable.

b) Explain why the attribute is not a local variable.

c) How is each method of the class able to access the attribute?

Model 3 Object-Oriented

Edit the class further to include the variable , the method , and

the modiﬁed block of code. Note that class variables (like ) are typically

deﬁned before the method.

... previous methods from Model 2 ...

Questions (15 min) Start time:

16. Examine the method (from Model 1):

a) Identify the three main variables used in :

b) For each variable, what is its scope? (local or global)

17. What determines whether a variable is deﬁned as an attribute or a local variable?

18. Now examine the method (from Model 3).

a) What variable was initialized in the class outside the constructor and methods?

b) How does the syntax of a class variable differ from an attribute (instance variable)?

19. Would it be possible to rewrite the method as a global function instead? If

so, explain how the function would differ.

20. How would you rewrite the line to call the global function

deﬁned in the previous question?

21. Consider the built-in class:

a) Given the statement , what data is stored in the object?

b) Show an example line of code that calls the method on the object .

c) If the method were deﬁned as a global function instead, how would you call it?

22. Based on the previous two questions, explain what the term “object-oriented” means.

23. Summarize the advantages you perceive for writing code as methods in classes instead of

global functions.

Extending Classes

A major beneﬁt of object-oriented programming is the ability to inherit classes and eliminate

duplicate code. Inheritance allows you to deﬁne a new class based on an existing class.

Content Learning Objectives

After completing this activity, students should be able to:

• Read and interpret UML class diagrams for an existing code base.

• Evaluate pros and cons for designs with multiple similar classes.

• Deﬁne inheritance and demonstrate how to extend a base class.

Process Skill Goals

During the activity, students should make progress toward:

• Working with all team members to reach consensus on hard questions. (Teamwork)

Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Model 1 UML Class Diagrams

Uniﬁed Modeling Language (UML) provides a standard way of visualizing how programs are

designed (http://www.uml.org/what-is-uml.htm). For example, a class diagram is a graphical

summary of the attributes and methods of a class.

Cow

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

respire()

speak()

Horse

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

nuzzle(position : tuple)

respire()

speak()

Lion

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

respire()

speak()

Pig

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

respire()

speak()

wallow()

Questions (15 min) Start time:

1. Draw an arrow from each name in the diagram to where it’s deﬁned in the code.

2. What are the attributes of ? What are the methods of ?

3. What is listed in each section of the UML class diagram?

a) Top section: b) Middle section: c) Bottom section:

4. Consider the following class diagrams:

Cow

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

respire()

speak()

Horse

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

nuzzle(position : tuple)

respire()

speak()

Lion

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

respire()

speak()

Pig

position : tuple

respired : int

stomach : list

__init__()

eat(item : str)

move(delta : tuple)

respire()

speak()

wallow()

a) What attributes do the classes have in common?

b) What methods do the classes have in common?

c) What methods are unique to a particular class?

5. Quickly examine the source code for each of the classes to identify similarities and differ-

ences. Write one or two words in each table cell to summarize your ﬁndings.

Cow Horse Lion Pig

eat

grass

move

walked

nuzzle

N/A

respire

nostrils

speak

moo

wallow

N/A

6. Consider what it would take to add a new method named to each of the classes.

a) Describe the process of adding the same method to each source ﬁle.

b) If a mistake is found later on, how would you correct the method?

c) What problems do you see with this approach as more classes are added?

Model 2 Single-Class Approach

Given that the classes from Model 1 are similar, we could try combining them into a single class.

In order to keep track of differences, we would need to store additional attributes. We could

provide the information from Question #5 when creating an object:

The UML diagram below outlines this approach. As a team, discuss this design and become

familiar with the accompanying source code.

Animal

eats_only : str

moved : str

name : str

nasal : str

position : tuple

respired : int

sound : str

stomach : list

__init__(name : str, eats_only : str, moved : str, nasal : str, sound : str)

eat(item : str)

move(delta : tuple)

nuzzle(position : tuple)

respire()

speak()

wallow()

Questions (10 min) Start time:

7. Circle the three original attributes that were deﬁned in Model 1.

8. Circle the two methods that were NOT common to all four classes in Model 1.

9. Write a statement that creates an object representing a lion. Assign it to a variable

named .

10. What methods does now have that it did not have in Model 1?

11. Describe 1–2 advantages the Model 2 design has compared to Model 1.

12. Describe 1–2 disadvantages the Model 2 design has compared to Model 1.

Model 3 Derived Classes

We can improve the code from Model 2 by using derived classes for , , , and .

These classes only contain the attributes and methods speciﬁc to them. is a base class

that contains attributes and methods they all have in common. This language feature is known

as inheritance, because derived classes “inherit” attributes and methods from the base class.

The UML diagram below outlines this approach. As a team, discuss this design and become

familiar with the accompanying source code.

Animal

eats_only : str

moved : str

name : str

position : tuple

respired : int

sound : str

stomach : list

__init__(name : str, eats_only : str, moved : str, sound : str)

eat(item : str)

move(delta : tuple)

respire()

speak()

Cow

__init__()

Horse

__init__()

nuzzle(position : tuple)

respire()

Lion

__init__()

Pig

__init__()

respire()

wallow()

Questions (20 min) Start time:

13. Open the source ﬁle. How many methods are deﬁned in the class? List the

name of each one.

14. Type the following code into a Python Shell (in the same location as the source ﬁles). What

methods are listed in the help?

15. Write a statement that creates a object. Assign it to a variable named . How is

this statement different from Question #9?

16. In a Python Shell, what is the value of ? Where did this value come from?

17. Does have any methods that it did not have in Model 1? Justify your answer.

18. Based on the source ﬁles, how does the method of differ from the

methods of the derived classes?

19. What is the meaning of the built-in function that is used in the derived classes?

20. Describe 1–2 advantages the Model 3 design has compared to Model 2.

Recursive Functions

Sometimes when solving a problem, we can compute the solution of a simpler version of the

same problem. Eventually we reach the most basic version, for which the answer is known.

Content Learning Objectives

After completing this activity, students should be able to:

• Identify the base case and recursive step of the factorial function.

• Trace a recursive function by hand to predict the number of calls.

• Write short recursive functions based on mathematical sequences.

Process Skill Goals

During the activity, students should make progress toward:

• Evaluating mathematical functions to gain insight on recursion. (Information Processing)

mons Attribution-NonCommercial-ShareAlike 4.0 International License.

Model 1 Factorial Function

”In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all

positive integers less than or equal to n. For example, 5! = 5 × 4 × 3 × 2 × 1 = 120.”

Source: https://en.wikipedia.org/wiki/Factorial

n n!

0 1

1 1

2 2

3 6

4 24

5 120

Questions (15 min) Start time:

1. Consider how to calculate 4! = 24.

a) Write out all the numbers that need to be multiplied:

4! =

b) Rewrite the expression using 3! instead of 3 × 2 × 1:

4! =

2. Write expressions similar to #1b showing how each factorial can be calculated in terms of a

smaller factorial. Each answer should end with a factorial (!).

a) 2! =

b) 3! =

c) 100! =

d) n! =

3. What is the value of 0! based on Model 1? Does it make sense to deﬁne 0! in terms of a

simpler factorial? Why or why not?

100

If we repeatedly break down a problem into smaller versions of itself, we eventually reach a basic

problem that can’t be broken down any further. Such a problem, like 0!, is referred to as the base case.

4. Consider the following Python function that takes n as a parameter and returns n!:

a) Review your answer to #2c that shows how to compute 100! using a smaller factorial.

Convert this expression to Python by using the function above instead of the ! operator.

b) Now rewrite your answer to #2d in Python using the variable and the function above.

c) In the source code above, replace the “1” on Line 6 with your answer from b). Then cross

out Lines 7 and 8. Test the resulting function in a Python Shell. Does it still work?

d) What speciﬁc function is being called on Line 6?

e) Why is the statement required on Line 3?

5. A function that refers to itself is called recursive. What two steps were necessary to deﬁne

the recursive version of ?

6. Was a loop necessary to cause the recursive version of to run multiple times?

Explain your reasoning.

101

Model 2 Fibonacci Numbers

The Fibonacci numbers are a sequence where every number (after the ﬁrst two) is the sum of

the two preceding numbers: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, . . .

Source: https://en.wikipedia.org/wiki/Fibonacci_number

We can deﬁne a recursive function to compute Fibonacci numbers. Enter the following code

into a Python Editor, and run the program to see the sequence.

Questions (10 min) Start time:

7. Based on the source code:

a) How many function calls are needed to compute ? Identify the value of the

parameter for each of these calls.

b) How many function calls are needed to compute ? Identify the value of the

parameter for each of these calls.

c) How many function calls are needed to compute ? Identify the value of the

parameter for each of these calls.

8. Check your answers for the previous question by adding the following statements to

the code and rerunning the program:

• Insert at Line 2, before the comment

• Insert at Line 10, before the statement

102

9. What happens if you try to compute in the Python Shell?

10. How could you modify the code so that this situation doesn’t happen?

Model 3 Summation

”In mathematics, summation (capital Greek sigma symbol: Σ) is the addition of a sequence of

numbers; the result is their sum or total.”

100

∑

i=1

i = 1 + 2 + 3 + . . . + 100 = 5050

Source: https://en.wikipedia.org/wiki/Summation

Questions (20 min) Start time:

11. Consider how to calculate

∑

i=1

i = 10.

a) Write out all the numbers that need to be added:

∑

i=1

i =

b) Show how this sum can be calculated in terms of a smaller summation.

∑

i=1

i =

12. Write an expression similar to #11b showing how any summation of n integers can be

calculated in terms of a smaller summation.

∑

i=1

i =

13. What is the base case of the summation? (Write the complete formula, not just the value.)

103

Here are important questions to consider before writing a recursive function:

• How can you deﬁne the problem in terms of a smaller similar problem?

• What is the base case, where you solve an easy problem in one step?

• For the recursive call, how will you make the problem size smaller?

To avoid inﬁnite recursion, make sure that each recursive call brings you closer to the base case!

14. Implement a recursive function named that takes a parameter and returns the

sum 1 + 2 + . . . + n. It should only have an statement and two statements (no loops).

15. Enter your code into a Python Editor, and test the function. Make sure that

correctly returns 5050.

16. Implement a recursive function named that takes three parameters ( , , and )

and returns the sum “a + ar + ar

+ ar

. . .” where n + 1 is the total number of terms.

a) What is the base case?

returns:

b) What is the recursive case?

returns:

c) Write the function in Python:

17. Enter your code into a Python Editor, and test the function. For example, if a = 10 and r = 3,

the ﬁrst ﬁve terms would be 10, 30, 90, 270, and 810. Make sure that

correctly returns 1210 (the sum of those ﬁve terms).

104

Appendix

105

M A N A G E R

• Helps the team get started quickly and remain focused.

◦ “I think we have everything; are we ready to begin?”

◦ “We're getting off topic; could we talk about that later?”

• Takes care of time management; keeps an eye on the clock.

◦ “I think we need to focus on _____ so we complete this section on time.”

◦ “Let's skip this question for now until we can ask the instructor for help.”

◦ “We have _____ minutes before we need to discuss. Let’s get this done.”

• Makes sure that all voices in the team are heard and respected.

◦ “(Name), would you be willing to read question _____ out loud?”

◦ “(Name), what do you think about our team's answer to _____?”

P R E S E N T E R

• Communicates questions and clarifications with the instructor and other teams.

◦ “Our team is confused about how _____ relates to _____.”

◦ “Would you explain what question _____ means by _____?”

• Ensures that all team members reach consensus before asking outside sources.

◦ “Does anyone in our team know the answer for _____?”

◦ “Before we ask the instructor, could someone clarify _____?”

◦ “Does everyone agree that we need to find out _____?”

• Presents conclusions of the team to the class, when requested by the instructor.

◦ “How should I explain this idea when asked to report out?”

◦ “Our team found the answer to number _____ by _____.”

106

R E C O R D E R

• Records the important aspects of group discussions, insights, etc.

◦ “This seems like an important conclusion to write down.”

◦ “Let’s stop for a minute so I can get this into our report.”

• Guides consensus building process; helps team agree on responses.

◦ “Would you all agree that _____ is a good answer for number _____?”

◦ “Is our answer completely supported by the explanation we gave?”

◦ “Would that response make sense to someone from another team?”

• Ensures that accurate revisions happen after class discussions.

◦ “Lets go back and revise what we wrote down for question _____.”

◦ “What did other teams say that we should include in our report?”

R E F L E C T O R

• Observes team dynamics and behavior with respect to the learning process.

◦ “I think what (name) said earlier is important; would you repeat that?”

◦ “Let’s wait for (name) to finish writing that down before we move on.”

• Reports to the team periodically during the activity on how the team performs.

◦ “We're doing really well right now by including all team members.”

◦ “I have a suggestion on how we could be more productive as a team.”

◦ “What process skills are we doing well? What do we need to improve?”

• Be ready to report to the entire class about how well the team is operating.

◦ “Overall, how effective would you say that our team was today?”

◦ “We found that when _____ happens, it works better if we _____.”

107

Meta Activity: Team Roles

Decide who will be what role for today; we will rotate the roles each week. If you have only

three people, one should have two roles. If you have ﬁve people, two may share the same role.

Manager:

Presenter:

Recorder:

Reﬂector:

Questions (15 min) Start time:

1. What is the difference between bold and italics on the role cards?

2. Manager: invite each person to explain their role to the team. Recorder: take notes of the

discussion by writing down key phrases next to the table above.

3. What responsibilities do two or more roles have in common?

4. For each role, give an example of how someone observing your team would know that a

person is not doing their job well.

• Manager:

• Presenter:

• Recorder:

• Reﬂector:

108

Meta Activity: Team Disruptions

Common disruptions to learning in teams include: talking about topics that are off-task, team-

mates answering questions on their own, entire teams working alone, limited or no commu-

nication between teammates, arguing or being disrespectful, rushing to complete the activity,

not being an active teammate, not coming to a consensus about an answer, writing incomplete

answers or explanations, ignoring ideas from one or more teammates.

Questions (10 min) Start time:

1. Pick four of the disruptions listed above. For each one, ﬁnd something from the role cards

that could help improve the team’s success. Use a different role for each disruption.

a) Manager:

b) Presenter:

c) Recorder:

d) Reﬂector:

109

Meta Activity: What Employers Want

The following table is from the Job Outlook 2019 survey by the National Association of Colleges

and Employers (NACE). A total of 172 organizations responded to the survey.

Attributes Employers Seek on a Candidate’s Resume

Attribute % of respondents

1. Communication skills (written) 82.0%

2. Problem-solving skills 80.9%

3. Ability to work in a team 78.7%

4. Initiative 74.2%

5. Analytical/quantitative skills 71.9%

6. Strong work ethic 70.8%

7. Communication skills (verbal) 67.4%

8. Leadership 67.4%

9. Detail-oriented 59.6%

10. Technical skills 59.6%

Source: https://www.naceweb.org/talent-acquisition/candidate-selection/

Questions (10 min) Start time:

1. Consider the top three attributes. Why do you think they are the most sought-after?

2. How is communication (written and verbal) related to problem solving and teamwork?

3. Which of these skills do each of you individually need to work on? Justify your answers.

4. How will you develop these skills in college: in courses, or other activities? Be speciﬁc.

110

Meta Activity: Group vs Team

Throughout the course, you will need to examine and process information, ask and answer

questions, construct your own understanding, and develop new problem-solving skills.

Questions (10 min) Start time:

1. What are some advantages to working in groups/teams?

2. What are some disadvantages to working in groups/teams?

3. What is the difference between a group and a team? Come up with a precise answer.

4. How can working as a team help you accomplish the tasks described above? Give at least

two speciﬁc examples.

111

Meta Activity: POGIL Research

Process-Oriented Guided Inquiry Learning (see pogil.org) is a student-centered, group-learning

instructional strategy and philosophy developed through research on how students learn best.

The following two ﬁgures are from peer-reviewed articles published in education journals.

Questions (10 min) Start time:

1. How large were the classes at each of the universities shown above?

2. What are the measures of performance shown in each of the ﬁgures?

3. What does the ﬁgure on the left suggest about POGIL’s impact on student success?

4. What does the ﬁgure on the right suggest about students’ retention of knowledge?

112

Case Study: Panic Attack

Frank was behind in his programming assignment. He approached Martin to see if he could

get some help. But he was so far behind and so confused that Martin just gave him his code

with the intent that he would “just look at it to get some ideas.”

In the paraphrased words of Frank: “I started the assignment three days after you put it up.

But then other assignments came in and I started on them too. I felt like I was chasing rabbits

and began to panic. It was already past the due date and I got really scared. That’s when I went

to Martin to see if he could help.” Frank copied much of the code and turned it in as his own.

Questions (10 min) Start time:

1. Which, if any, of the students were at fault? Why?

2. Which speciﬁc Honor Code violations occurred?

3. What should Martin have done in this situation?

4. What options did Frank have besides cheating?

113

Case Study: A Friend Indeed

Jeffrey was having trouble with one of the last programming assignments. He didn’t even know

where to begin and it was already late. Another student, Stephen, lived in his hall and Jeff was

pretty friendly with him. Jeff went to Stephen’s room and told him that his computer was acting

ﬂaky. He asked if could he borrow Stephen’s laptop to ﬁnish up the program? Stephen was on

his way out to dinner and told him okay. When he got back Jeffrey was gone.

While Stephen was out, Jeffrey searched for and located the code for the assignment on Stephen’s

machine. Jeffrey copied it onto his ﬂash drive and took it back to his room, where he modiﬁed

the code a bit before submitting it for a grade.

Questions (10 min) Start time:

1. Which, if any, of the students were at fault? Why?

2. Which speciﬁc Honor Code violations occurred?

3. What should Stephen have done in this situation?

4. What options did Jeffrey have besides cheating?

114

Case Study: Oops!

Emily was working in the lab on her programming assignment. She ﬁnished the program,

submitted it, and went on to do some other work. Shortly thereafter, she left the lab.

Another student, Kyle, was working nearby. He knew that Emily had successfully submitted

the assignment, and he had not been able to get his to work properly. When Emily left, he

noticed that she had not logged out of her computer. He moved to her workstation, found the

work under her Documents directory, and copied it onto his ﬂash drive. He then logged out,

logged in as himself, and copied the code onto his Desktop where he modiﬁed the program a

bit, then successfully submitted it.

Questions (10 min) Start time:

1. Which, if any, of the students were at fault? Why?

2. Which speciﬁc Honor Code violations occurred?

3. What should Emily have done in this situation?

4. What options did Kyle have besides cheating?

115

Case Study: Too Close for Comfort

Bill and Jeff were two freshman rooming together in the fall semester and were taking CS 139.

Bill was an excellent student for whom the work in CS 139 seemed to come easily. Jeff seemed

to struggle a bit more, but was able to do the work and turned most labs and programs in on

time.

Both programs came in looking virtually the same. When confronted, Jeff claimed the work

as his own and stated that he did not know how the code from the roommates was the same.

Later Bill told the professor that while programming was easy for him, he had struggled with

another class and then got behind with this program. He didn’t think the professor would ﬁnd

out and so stole his roommate’s code and turned that in.

Questions (10 min) Start time:

1. Which, if any, of the students were at fault? Why?

2. Which speciﬁc Honor Code violations occurred?

3. What should Jeff have done in this situation?

4. What options did Bill have besides cheating?

116

Case Study: Let’s Make a Deal

It was mid-semester and the pressure was on, not only in CS but in other classes. Jamie and Pat

were each working on the programming assignment in the lab, but neither was having much

success. Jamie had started several days ago, but he was having trouble debugging his current

work. Pat had just started that day and knew that she would be turning it in late. Regardless,

Pat offered to help Jamie work out the problems with his code.

Together, and after a couple of hours of work, they got the program to work. Pat said, “Now

that yours is working, can you give me the code so that I can also get credit for this assignment?”

When Jamie objected, Pat said, “Hey, you wouldn’t have gotten it ﬁnished if it weren’t for my

help, and now mine will be even later!” So Jamie turned over a copy of the code. Pat made

some changes to a few sections, and then turned in the ﬁnal program.

Questions (10 min) Start time:

1. Which, if any, of the students were at fault? Why?

2. Which speciﬁc Honor Code violations occurred?

3. What should Pat have done in this situation?

4. What should Jamie have done in this situation?

117

Case Study: A Friendly Assist

George was struggling with the programming assignment on the night it was due. He had

gone home over the weekend before, thinking that it would be easy to do this assignment, but

it turned out to be more difﬁcult than he thought. After working on some parts of it and giving

up in frustration, he turned to Shelley, a senior CS student who had taken the course several

semesters before. He showed Shelley the assignment, and the two of them worked on it late

into the night. They successfully submitted the program with a late penalty of only one day.

Questions (10 min) Start time:

1. Which, if any, of the students were at fault? Why?

2. Which speciﬁc Honor Code violations occurred?

3. What should Shelley have done in this situation?

4. What options did George have besides cheating?

118

Case Study: A Team Effort

Stan, Jane, and Tom were part of a project team. At the start of the semester they all agreed to

be responsible for everything that was submitted by their project. As the project got underway,

they divided up the work and decided to complete and submit the three parts individually.

Tom was behind on his work as the deadline approached, and so as not to be late he copied

several pages from ﬁles of a roommate who had completed the same work last year. The team

project was submitted on time, though only 2/3 of it was original work.

Questions (10 min) Start time:

1. Which, if any, of the students were at fault? Why?

2. Which speciﬁc Honor Code violations occurred?

3. What options did Tom have besides cheating?

4. Should all three students be penalized? Why or why not?

119