Variables

Variables

• a variable is a name that refers to a value:
• once a variable is declared and assigned a value, you can use that variable where you would use any other values →
  • my_variable + "!"
  • print(my_variable)
  • (a + b) / c

Assignment

• use the assignment operator: =
  • a single equals sign
  • note - does not test for equality, performs assignment!
• variable name goes on the left
• value goes on the right

Using Variables

When do you use variables?

• when you want your program to remember a value
• if you have a value that will vary
• some examples include:
  • a player's score
  • a count of repetitions
  • user input
  • sensor input
• additionally, using variables will help make your code more maintainable / less brittle
  • (let's talk about this…)

Here's an Example of Improving Maintainability

Let's say you have a program that adds x number of exclamation points to some words. →

print("foo" + "!" * 5)
print("bar" + "!" * 5)

my_exclamation_constant = 5
print("foo" + "!" * my_exclamation_constant)
print("bar" + "!" * my_exclamation_constant)

"Hardcoding"

• assume everything will vary / change
• avoid using a bare literal
  • you remember what that is, right?
  • "a string", 58.3
• sometimes this is called hardcoding
• cleaning this stuff up helps code reuse / DRY
  • not having to write the same thing multiple times
  • don't repeat yourself
• we saw that in the previous slide

Multiple Assignment

You can also assign multiple values to multiple variable names simultaneously. →

This is done by:

• using the assignment operator: =
• a comma separated group of variables on the left-hand side
• a comma separated group of values on the right hand side

a, b, c = 3, 21, 7

Each variable/value is bound in the order that they appear.

Multiple Assignment Continued

a, b, c = 3, 21, 7

What values are referred to by a, b, and c? →

a -> 3
b -> 21
c -> 7

Here's a Quick Exercise on a Tiny Algorithm

If I have two variables, a and b, and they are set to 3 and 21 respectively, how would I swap their values in code? (Try this on your own!) →

a = 3
b = 21
print("a:", a, "b:", b)
c = b
b = a
a = c
print("a:", a, "b:", b)

An Idiomatic Way to Do It

Here's another, more idiomatic way to do it

a = 3
b = 21
a, b = b, a

…And, Some BTWs

• in Python, if something is idiomatic, it's called Pythonic
• someone that codes in Python is sometimes called a Pythonista
• (yes, really)

Greeaaat. Maybe we can use them to help us create our own functions!