Operators

An operator is a symbol that does something with values. You have already seen + and =. Python has a few more that are worth knowing early.

Arithmetic operators

a = 17
b = 5

print(a + b)    # addition
print(a - b)    # subtraction
print(a * b)    # multiplication
print(a / b)    # division always gives a float
print(a // b)   # floor division drops the decimals
print(a % b)    # remainder (modulo)
print(a ** 2)   # power

22
12
85
3.4
3
2
289

Assignment shortcuts

Instead of writing x = x + 3, you can write x += 3. The same works for the other arithmetic operators.

steps = 100
steps += 50
steps -= 20
steps *= 2
print(steps)

260

Comparison operators

Comparisons answer a yes-or-no question, so they always give a bool.

print(10 == 10)
print(10 != 7)
print(3 < 8 <= 8)   # Python lets you chain comparisons
print("apple" < "banana")

True
True
True
True

Strings are compared letter by letter, in dictionary order.

Logical operators

and is true only when both sides are true. or is true when at least one side is. not flips a value.

is_weekend = True
is_raining = False

print(is_weekend and not is_raining)
print(is_weekend or is_raining)
print(not is_weekend)

True
True
False

Order of operations

Python follows the usual maths rules: brackets first, then **, then *, /, //, %, and finally + and -. When in doubt, add brackets. They also make code easier to read.

print(2 + 3 * 4)
print((2 + 3) * 4)
print(-2 ** 2)

14
20
-4

The last line surprises many people: ** happens before the minus sign, so it means -(2 ** 2).