Error when trying to overload an operator "/"

Question

I recently start teaching myself game programming. Someone recommend me to start with Python and I got the book "Beginning game development with Python and Pygame: From novice to professional". I got to a part where they teach about Vectors and creating a Vector2 class. Everything was going well until I tried to overload the division operator. My code goes like this:

class Vector2(object): def __init__(self, x=0.0, y=0.0): self.x = x self.y = y def __str__(self): return "(%s, %s)"%(self.x, self.y) @classmethod def from_points(cls, P1, P2): return cls(P2[0] - P1[0], P2[1] - P1[1]) def __add__(self,rhs): return Vector2(self.x + rhs.x, self.y + rhs.y) def __sub__(self,rhs): return Vector2(self.x - rhs.x, self.y - rhs.y) def __mul__(self, scalar): return Vector2( self.x*scalar, self.y*scalar) def __div__(self, scalar): return Vector2( self.x/scalar, self.y/scalar)

Now, when I tried to call the "/" operator, this shows up:

AB = Vector2(10.0,25.0) print(AB) # <<<<(10.0, 25.0) v1 = AB + Vector2(20.,10.) print(v1) # <<<<(30.0, 35.0) v2 = AB - Vector2(20.,10.) print(v2) # <<<<(-10.0, 15.0) v3 = AB * 3 print(v3) # <<<<(30.0, 75.0) print(v3 / 3) TypeError: unsupported operand type(s) for /: 'Vector2' and 'int'

This was all in Python 3.3 but if I run it with Python 2.7, everything works correctly. Where's the problem?

see docs.python.org/3/library/operator.html#operator.__truediv__ — zhangxaochen
– zhangxaochen, Commented Feb 18, 2014 at 16:25
I'm sure I'll get to know what is numpy. But, well, I'm trying to learn this stuff from Python. I have zero experience with it. — darkwatcher5
– darkwatcher5, Commented Feb 18, 2014 at 16:33

vallentin · Accepted Answer · 2017-05-27 13:27:51Z

87

In Python 3.x, you need to overload the __floordiv__ and __truediv__ operators, not the __div__ operator. The former corresponds to the // operation (returns an integer) and the latter to / (returns a float).

edited May 27, 2017 at 13:27

vallentin

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answered Feb 18, 2014 at 16:23

isedev

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3 Comments

darkwatcher5 Over a year ago

I just tested it and it works! Thanks for the answer. I'll have to do some reading on the docs.

Adam Smith Over a year ago

@darkwatcher5 in python2, the result of integer division was always an integer. This means 5/2 == 2, though 5/2.0 == 2.5. Python3 changed that (due to the principle of least astonishment) and replaced __div__ with __floordiv__ (which is 5//2 == 2) and __truediv__ (which is 5/2 == 2.5)

darkwatcher5 Over a year ago

@adsmith Seems really useful to be honest. And much specific.

kelm · Accepted Answer · 2014-02-18 16:23:35Z

In Python 3, the division operators are called __truediv__ and __floordiv__. See the Data model documentation for more information.

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