In Python, about the remainder using a negative number.

Python Code

 print (-7%2) #1
print(-7%3)#2
print(7%-2)#-1
print(-7%3)#2
print(7%-3)#-2

But don't you know why?

python

2022-09-30 21:48

The reason is, "That's what I decided to do."Specification: The division of integers is rounded in a negative infinite direction.
(2)

of https://docs.python.org/ja/3/library/stdtypes.html

Also, if (x//y)*y+(x%y)=x is not present, the remainder will inevitably be determined.

This behavior shows questions tagged with c or python, this is the decision you made.

# I want to know why Oira decided to do so.

2022-09-30 21:48

First of all, Python interprets the monomial minus - over % as priority, so for example -7%2 is not (-7)%2.

Python's remainder operator % returns the remainder of the second argument and the same symbol.Therefore, (-7)%2 returns 1, while 7%(-2) returns -1.

The specifications for this "bonding priority" and "remaining negative numbers" vary by programming language, so check the documentation first.

*Supplement: Why -7%3 is 2

This is about mathematics before Python, but if you write -7=3*(-3)+2, the remainder is 2.
You can also take -7=3*(-2)-1 and make the remainder -1, which gives you a choice.
Similarly, there are several ways that 7%-3 and -7%-3 can be handled in a uniform manner, and different languages can be used in different ways.

2022-09-30 21:48

In Python, about the remainder using a negative number.

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