Why Does Python's Modulo Operator Produce a Positive Result with Negative Numbers?

Python Modulo Operator Behavior with Negative Numbers

The modulo operator (%) in Python handles negative numbers differently than in C or C . Unlike those languages, Python's modulo operator always ensures that the result has the same sign as the denominator.

Why -5 % 4 Evaluates to 3, Not -1

Consider the expression -5 % 4. In this case, it evaluates to 3 because the calculation proceeds as follows:

• (-5) / 4 = -1.25 (floating-point division)
• Floor(-1.25) = -2 (removes the fractional part)
• (-5) % 4 = (-2 × 4 3) % 4 = 3

Python chooses this behavior because a nonnegative result is generally more useful. For example, when computing week days using the formula (2 - N) % 7, the modulo operator ensures the result falls within the range [0, 6], representing the days of the week.

Contrast with C Behavior

In C, if N is greater than or equal to 3 in this formula, the result would be negative, which is not a valid day number. To obtain a correct result, C requires manual adjustment by adding 7 to the negative result.

For further information on the behavior of the modulo operator with negative numbers in different languages, please refer to the Wikipedia article on the modulo operator.

The above is the detailed content of Why Does Python's Modulo Operator Produce a Positive Result with Negative Numbers?. For more information, please follow other related articles on the PHP Chinese website!