On Fri, 3 Apr 2009 at 17:57, Paul Moore wrote:
In fact, Python seems to be doing something I don't understand:
class Element(object):
... def __init__(self, key, id):
... self.key = key
... self.id = id
... def __eq__(self, other):
... print "Calling __eq__ for %s" % self.id
... return self.key == other
... def __hash__(self):
... return hash(self.key)
...
a = Element('k', 'a')
b = Element('k', 'b')
a == b
Calling __eq__ for a
Calling __eq__ for b
True
a == a
Calling __eq__ for a
Calling __eq__ for a
True
Why does __eq__ get called twice in these cases? Why does a == b, as
that means a.key == b, and clearly a.key ('k') does *not* equal b. Or
are there some further options being tried, in str,__eq__ or
object.__eq__? The documentation doesn't say so... Specifically,
there's nothing saying that a "reversed" version is tried.
a == b
So, python calls a.__eq__(b)
Now, that function does:
a.key == b
Since b is an object with an __eq__ method, python calls
b.__eq__(a.key).
That function does:
a.key == b.key
ie: the OP's code is inefficient :)
--David
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