Shortcuts and Precedence

Big idea

Shortcut assignments like += update a variable in place. Precedence decides which operator goes first when several share a line.

Shortcut assignment

score = score + 10 is so common that Python has a shorter way to say it:

score = 10
score += 5
score *= 2
score -= 1
print(score)

29

They work on strings too: name += "!" adds an exclamation mark.

Python has no ++ or --. Write count += 1.

Watch it

Precedence: who goes first

Just like in school maths, * happens before +:

print(2 + 3 * 4)      # 14, not 20
print((2 + 3) * 4)    # 20 — parentheses go first

From first to last:

1. ( ) — parentheses
2. ** — power
3. -x — a negative sign
4. *, /, //, %
5. +, -
6. comparisons: ==, !=, <, >, <=, >=
7. not
8. and
9. or

print(10 - 4 - 3)
print(2 * 3 ** 2)
print(-2 ** 2)
print(1 + 2 == 3)

3
18
-4
True

Two surprises: ** goes before the minus sign, so -2 ** 2 is -(2 ** 2) = -4. And arithmetic happens before ==, so 1 + 2 == 3 compares 3 with 3.

When in doubt, add parentheses

a = 80
b = 90
print(a + b / 2)

output
85.0

Parentheses cost nothing and make your intent obvious to the next reader — who is usually you, next week.

Think of it like

The order you get dressed in. Socks before shoes, whatever order you say them. Parentheses are you saying "no — this one first".

Key terms

• Augmented assignment — Shortcuts like += that update a variable.
• Precedence — Which operator is applied first.
• Parentheses — Force part of an expression to be worked out first.