CODEWITHSUNDEEP
pythonpython-3.xpython-3.2
Jul
Jul

Reputation: 549

Python 3.2.2 custom object comparation fails

I have a python class declared like the following within a module

class Position:
def __init__(self, x, y):
    self.x = int(x)
    self.y = int(y)
def __str__(self):
    return self.toString()
def toString(self): #deprecated
    return "{x:"+str(self.x)+" y:"+str(self.y)+"}"

Now, later in the main program, I do a comparation like this:

can_pos = somestreet.endOfStreet(curPos).getPos() #returns a Position object
if(can_pos == atPos): # this returns False
  #blafoo
#if(can_pos.x == atPos.x and can_pos.y == atPos.y): #this returns True (and is expected)

I do not understand what the reason for the different behaviour could be ...

It would be very nice if someone could give me a hint on that :)

Thanks in advance

Upvotes: 0

Views: 191

Answers (1)

DSM
DSM

Reputation: 353059

As noted in the comments, you need to define at least __eq__ and __ne__ explicitly:

class Position:
    def __init__(self, x, y):
        self.x = int(x)
        self.y = int(y)
    def __eq__(self, other):
        return self.x == other.x and self.y == other.y
    def __ne__(self, other):
        return not self == other

which gives

>>> a = Position(1,2)
>>> b = Position(1,2)
>>> c = Position(2,3)
>>> a == b
True
>>> a == c
False
>>> b == c
False
>>> a != a
False
>>> a != b
False
>>> a != c
True

Note, however, than in Python 2, you'll have:

>>> a > c
True

and other possibly undesirable behaviours, whereas in Python 3 (which you're using) you'll get 

TypeError: unorderable types: Position() > Position()

Upvotes: 3

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