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Variables, expressions and statements: variables

Learning outcomes

For teachers

Teaching goals are:

  • Learners have worked with variables
  • Learners understand the purpose of variables
  • Learners have obtained the data type of a variable
  • Learners have heard about what a data type is
  • Learners have practiced converting an equation and a text question to Python

Lesson plan:

Exercises:

  • 5 mins: prior knowledge
  • 5 mins: presentation
  • 15 mins: challenge
  • 5 mins: feedback

Prior questions:

  • What is a data type?
  • Can you name a Python data type?
  • What is an object?
  • What is a variable?
  • What are the rules for the name of a variable?
  • What are good practices for the name of a variable?
  • What is an operator?
  • Can you name an operator?

Overview

In any non-trivial calculation, we want to let our computer remember things, such as the content of a data file or the parameters/settings we use in our program. Variables allows one to make a computer store ('remember') information. Here we use our first simple variables.

Also we practice converting an equation and a mathematical problem to Python code. We will discover the helpful modulo operator.

Exercises

Exercise 1: working with variables

Learning outcomes

  • get the type of an object
  • create a variable
  • use a variable

Read the following sections of How to Think Like a Computer Scientist: Learning with Python 3:

  • 2.1. Values and data types
  • 2.2. Variables
  • 2.3. Variable names and keywords

Then in section 2.14, do exercises 1 to and including 4.

2.14.1

Take the sentence: 'All work and no play makes Jack a dull boy'. Store each word in a separate variable, then print out the sentence on one line using print.

Answer 
a = 'All'
b = 'work'
c = 'and'
d = 'no'
e = 'play'
f = 'makes'
g = 'Jack'
h = 'a'
i = 'dull'
j = 'boy'
print(a, b, c, d, e, f, g, h, i, j)

2.14.2

Add parenthesis to the expression 6 * 1 - 2 to change its value from 4 to -6.

Answer 
6 * (1 - 2)

2.14.3

Place a comment before a line of code in a script that previously worked, and record what happens when you rerun the program.

Answer

I use this code as a starting point:

a = 'All'
b = 'work'
c = 'and'
d = 'no'
e = 'play'
f = 'makes'
g = 'Jack'
h = 'a'
i = 'dull'
j = 'boy'
print(a, b, c, d, e, f, g, h, i, j)

Commenting out the first line:

    print(a, b, c, d, e, f, g, h, i, j)
          ^
NameError: name 'a' is not defined

Commenting out the last line results in no sentence being printed.

2.14.4

Start the Python interpreter and enter bruce + 4 at the prompt. This will give you an error:

NameError: name 'bruce' is not defined

Assign a value to bruce so that bruce + 4 evaluates to 10.

Answer

Here is a solution:

bruce = 6
print(bruce + 4)