python - What determines the sign of m % n for integers?

Question

The modulo in Python is confusing.

In Python, % operator is calculating the remainder:

>>> 9 % 5
4

However:

>>> -9 % 5
1

Why is the result 1? and not -4?

Answer 1

Because in python, the sign matches the denominator.

>>> 9 % -5
-1
>>> -9 % 5
1

For an explanation of why it was implemented this way, read the blog post by Guido.