The following piece of code
class point:
def __init__(self, x, y):
self.x = x
self.y = y
def dispc(self):
return ('(' + str(self.x) + ',' + str(self.y) + ')')
def __cmp__(self, other):
return ((self.x > other.x) and (self.y > other.y))
works fine in Python 2, but in Python 3 I get an error:
>>> p=point(2,3)
>>> q=point(3,4)
>>> p>q
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unorderable types: point() > point()
It only works for == and !=.
You need to provide the rich comparison methods for ordering in Python 3, which are __lt__, __gt__, __le__, __ge__, __eq__, and __ne__. See also: PEP 207 -- Rich Comparisons.
__cmp__ is no longer used.
More specifically, __lt__ takes self and other as arguments, and needs to return whether self is less than other. For example:
class Point(object):
...
def __lt__(self, other):
return ((self.x < other.x) and (self.y < other.y))
(This isn't a sensible comparison implementation, but it's hard to tell what you were going for.)
So if you have the following situation:
p1 = Point(1, 2)
p2 = Point(3, 4)
p1 < p2
This will be equivalent to:
p1.__lt__(p2)
which would return True.
__eq__ would return True if the points are equal and False otherwise. The other methods work analogously.
If you use the functools.total_ordering decorator, you only need to implement e.g. the __lt__ and __eq__ methods:
from functools import total_ordering
@total_ordering
class Point(object):
def __lt__(self, other):
...
def __eq__(self, other):
...