7.2 Arithmetic Operators

The standard mathematical operators, all usable on int and float (and some on other types, see 7.13 Operators with Different Data Types).

Addition (+)

>>> 5 + 3
8

Subtraction (-)

>>> 5 - 3
2

Multiplication (*)

>>> 5 * 3
15

Division (/)

What Is It?

True division — always returns a float, even if the result is a whole number.

>>> 5 / 3
1.6666666666666667

Floor Division (//)

What Is It?

Divides and rounds down to the nearest whole number.

Why Is It Used?

When a whole-number result is needed — e.g. “how many full batches of 3 fit into 5 items?”

>>> 5 // 3
1

Modulus (%)

What Is It?

Returns the remainder of division.

Why Is It Used?

Extremely common for “every Nth item” logic, and checking even/odd.

>>> 5 % 3
2

Exponent (**)

>>> 5 ** 3
125

Practical Example

>>> total_items = 17
>>> batch_size = 5
>>> full_batches = total_items // batch_size
>>> leftover = total_items % batch_size
>>> full_batches, leftover
(3, 2)

Quick Interview Answer

“Python’s arithmetic operators are + - * / // % **. The one that trips people up most is / vs //: / is true division and always returns a float, while // is floor division and rounds down to a whole number. % returns the remainder, which combined with // is the standard pattern for splitting a total into full batches plus a leftover.”

Common Mistakes

• Expecting / to return an int when both operands are int — it always returns a float in Python 3, unlike Python 2’s /, covered further in 7.14 Common Mistakes.
• Confusing // with rounding to the nearest whole number — it always rounds down (toward negative infinity), not to the nearest value.
• Forgetting ** is right-associative — 2 ** 3 ** 2 is 2 ** (3 ** 2) = 512, not (2 ** 3) ** 2, detailed in 7.9 Operator Precedence and Expression Evaluation.