Numbers and Operators

Python can work as a powerful calculator. It supports the usual arithmetic plus a few handy operators for whole-number maths.

Arithmetic operators

• + addition, - subtraction, * multiplication.
• / true division — always gives a float, so 6 / 2 is 3.0.
• // floor division — divides then drops the fraction, so 7 // 2 is 3.
• % modulo — the remainder, so 7 % 2 is 1.
• ** power, so 2 ** 3 is 8.

print(6 / 2)    # 3.0
print(7 // 2)   # 3
print(7 % 2)    # 1
print(2 ** 3)   # 8

Order of operations

Python follows normal maths rules: brackets first, then power, then multiply and divide, then add and subtract. Use round brackets to be clear:

print(2 + 3 * 4)      # 14
print((2 + 3) * 4)    # 20

Comparison operators

These compare two values and give a bool:

• == equal to, != not equal to.
• < less than, > greater than.
• <= less than or equal, >= greater than or equal.

print(5 == 5)   # True
print(5 != 3)   # True
print(4 <= 4)   # True

Shorthand assignment

Operators can combine with assignment to update a variable:

score = 10
score += 5   # same as score = score + 5, now 15
score -= 2   # now 13

The same idea works with *=, /= and others. These save you from writing the variable name twice.

Mixing integers and floats

When you combine an int with a float, the answer becomes a float:

print(3 + 1.0)   # 4.0
print(10 * 2.5)  # 25.0

This is why measurements are often kept as floats. (Money is better stored as whole cents in an int, because floats give small rounding errors.)

Rounding and helpers

Python has built-in helpers for common maths:

• round(x) rounds to the nearest whole number, so round(3.6) is 4.
• abs(x) gives the size without a sign, so abs(-7) is 7.
• round(x, 2) keeps two decimal places.

print(round(3.14159, 2))   # 3.14
print(abs(-5))             # 5

Chained comparisons

Python lets you write natural range checks in one go:

x = 5
print(1 < x < 10)   # True