Variables and numbers

A variable is a name that refers to a value. You create one with a single equals sign:

age = 12
name = "Sam"
print(name, "is", age)

Sam is 12

Read age = 12 as "age now refers to 12". The equals sign means assign, not "is equal to". The name goes on the left, the value on the right.

A variable can be given a new value at any time. The new value replaces the old one:

score = 0
print(score)
score = 10
print(score)
score = score + 5
print(score)

0
10
15

The last assignment looks odd at first. Python works out the right-hand side first (score + 5, which is 15), then stores the result back in score.

Variable names can contain letters, digits and underscores, but cannot start with a digit or contain spaces. Python programmers usually write names in lowercase with underscores between words:

total_price = 42
player_2_score = 7

Choose names that say what the value means. total_price is much easier to understand later than tp or x.

Python has whole numbers, called integers (int), and numbers with a decimal point, called floats (float). The type function tells you which one you have:

print(type(7))
print(type(7.5))

<class 'int'>
<class 'float'>

Plain division with / always gives a float, even when the answer is whole: 8 / 2 is 4.0. Use // when you want a whole number.

// and % are a useful pair. Together they split a number into "how many whole groups" and "how many left over":

eggs = 14
boxes = eggs // 6
left_over = eggs % 6
print(boxes, "full boxes and", left_over, "eggs left over")

2 full boxes and 2 eggs left over

Python follows the usual order of operations, so 2 + 3 * 4 is 14. Use brackets when you want something worked out first: (2 + 3) * 4 is 20.