Peter Otten wrote:
Ethan Furman wrote:
Peter Otten wrote:
Ethan Furman wrote:
Several folk have said that objects that compare equal must hash equal,
and the docs also state this
http://docs.python.org/dev/reference/datamodel.html#object.__hash__
--> class Wierd():
... def __init__(self, value):
... self.value = value
... def __eq__(self, other):
... return self.value == other
... def __hash__(self):
... return hash((self.value + 13) ** 3)
...
Try this:
d = {Wierd(1): 0}
1 in d
False
1 in d.keys()
True
My apologies -- I'm trying this in Python3:
Then you have to convert the keys to a list explicitly:
class Weird:
... def __init__(self, value):
... self.value = value
... def __eq__(self, other):
... return self.value == other
... def __hash__(self):
... return hash((self.value + 13) **3)
...
d = {Weird(1): 0}
1 in d
False
1 in d.keys()
False
1 in list(d.keys())
True
Ah!! The light finally dawned! Many thanks for everyone's input.
So if Wierd has a need to compare equal to some other type, it should
implement a .equals() method. Gotcha.
Likewise, if two different type's instances can compare equal, then for
the most part they should be interchangeable.
~Ethan~
--
http://mail.python.org/mailman/listinfo/python-list
