Ian Kelly wrote:
> As you found by searching, __reduce__ is used to determine how
> instances of the class are pickled. If the example you're using
> doesn't do any pickling, then it's not really relevant to the example.
> It's probably included so that it won't be missed when the code is
> copied.
__reduce__() also makes copying work as expected:
>>> class OrderedCounter(Counter, OrderedDict):
... 'Counter that remembers the order elements are first seen'
... def __repr__(self):
... return '%s(%r)' % (self.__class__.__name__,
... OrderedDict(self))
... def __reduce__(self):
... return self.__class__, (OrderedDict(self),)
...
>>> oc = OrderedCounter('abracadabra')
>>> import copy
>>> copy.copy(oc)
OrderedCounter(OrderedDict([('a', 5), ('b', 2), ('r', 2), ('c', 1), ('d',
1)]))
Now take away the __reduce__ method:
>>> del OrderedCounter.__reduce__
>>> copy.copy(oc)
OrderedCounter(OrderedDict([('b', 2), ('a', 5), ('c', 1), ('r', 2), ('d',
1)]))
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