On Fri, 23 Jul 2010 09:22:55 pm m...@doctors.net.uk wrote:
> Dear Tutors,
>
> I am tring to deal with some repeated data, and hence repeated
> objects (I construct objects from the data).
>
> I had hoped to use a set to uniquify the objects. However, I am
> having problems with defining uniqueness.
The objects need to define __eq__ and __hash__, and they must be
immutable.
The easy way to do so is to inherit from something which is already
immutable, say strings, ints, tuples or floats:
class MyObject(int):
"""Just like an int, but coloured purple."""
def __init__(self, *args):
self.colour = 'purple'
Otherwise, something like this recipe should do the job:
class MyObject(object):
def __init__(self, a, b):
self._value = (a, b) # Private attribute, don't touch this.
@property
def value(self):
return self._value
def __eq__(self, other):
if isinstance(other, MyObject): return self.value == other.value
return NotImplemented # Let the other object try.
def __ne__(self, other):
return not self == other
def __hash__(self):
return hash(self.value)
If x and y are instances of your class, and x equals y, then hash(x)
*must* equal hash(y). (The opposite doesn't apply though... if x and y
hash equal, they don't necessarily have to equal.)
--
Steven D'Aprano
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