Order of operations

Numbers & Math, lesson 3 of 5

🔢 Numbers & Math, lesson 3 of 5

Order of operations

How Python decides what to calculate first, plus handy shortcuts like +=.

8 min

2 exercises

2 quizzes

0/4 solved

Getting Python ready… examples can run in a moment.

Python follows the same rules as math class:

  1. ( ) parentheses first
  2. ** powers
  3. *, /, //, % from left to right
  4. + and - from left to right

When in doubt, add parentheses. They make your intention clear to both Python and people.

Example

Precedence in action

Add parentheses to the last line so it calculates (2 * 3) ** 2 instead.

Quiz

What does this print?

Exercise

Fix the temperature

To convert Fahrenheit to Celsius: subtract 32, then multiply by 5 and divide by 9. The formula below gives the wrong answer. Fix it so celsius is 100.0 for 212 °F.

Updating a variable with its own value is so common that Python has shortcuts called augmented assignment:

Shortcut Means
x += 3 x = x + 3
x -= 3 x = x - 3
x *= 3 x = x * 3
x /= 3 x = x / 3
Example

Shortcuts

Try points //= 4 and points **= 2 too.

Quiz

What does this print?

Exercise

Savings jar

Update savings using augmented assignment:

  1. add 20 with +=
  2. spend 5 with -=
  3. triple it with *=

It should end at 105.