diff options
Diffstat (limited to 'Lib/sets.py')
| -rw-r--r-- | Lib/sets.py | 32 |
1 files changed, 26 insertions, 6 deletions
diff --git a/Lib/sets.py b/Lib/sets.py index 0824fb1..e6a509f 100644 --- a/Lib/sets.py +++ b/Lib/sets.py @@ -102,20 +102,40 @@ class BaseSet(object): """ return self._data.iterkeys() - # Three-way comparison is not supported + # Three-way comparison is not supported. However, because __eq__ is + # tried before __cmp__, if Set x == Set y, x.__eq__(y) returns True and + # then cmp(x, y) returns 0 (Python doesn't actually call __cmp__ in this + # case). def __cmp__(self, other): raise TypeError, "can't compare sets using cmp()" - # Equality comparisons using the underlying dicts + # Equality comparisons using the underlying dicts. Mixed-type comparisons + # are allowed here, where Set == z for non-Set z always returns False, + # and Set != z always True. This allows expressions like "x in y" to + # give the expected result when y is a sequence of mixed types, not + # raising a pointless TypeError just because y contains a Set, or x is + # a Set and y contain's a non-set ("in" invokes only __eq__). + # Subtle: it would be nicer if __eq__ and __ne__ could return + # NotImplemented instead of True or False. Then the other comparand + # would get a chance to determine the result, and if the other comparand + # also returned NotImplemented then it would fall back to object address + # comparison (which would always return False for __eq__ and always + # True for __ne__). However, that doesn't work, because this type + # *also* implements __cmp__: if, e.g., __eq__ returns NotImplemented, + # Python tries __cmp__ next, and the __cmp__ here then raises TypeError. def __eq__(self, other): - self._binary_sanity_check(other) - return self._data == other._data + if isinstance(other, BaseSet): + return self._data == other._data + else: + return False def __ne__(self, other): - self._binary_sanity_check(other) - return self._data != other._data + if isinstance(other, BaseSet): + return self._data != other._data + else: + return True # Copying operations |