Change the binary operators |, &, ^, - to return NotImplemented rather
than raising TypeError when the other argument is not a BaseSet. This
made it necessary to separate the implementation of e.g. __or__ from
the union method; the latter should not return NotImplemented but
raise TypeError. This is accomplished by making union(self, other)
return self|other, etc.; Python's binary operator machinery will raise
TypeError.
The idea behind this change is to allow other set implementations with
an incompatible internal structure; these can provide union (etc.) with
standard sets by implementing __ror__ etc.
I wish I could do this for comparisons too, but the default comparison
implementation allows comparing anything to anything else (returning
false); we don't want that (at least the test suite makes sure
e.g. Set()==42 raises TypeError). That's probably fine; otherwise
other set implementations would be constrained to implementing a hash
that's compatible with ours.
diff --git a/Lib/sets.py b/Lib/sets.py
index eeef0e8..fee06d7 100644
--- a/Lib/sets.py
+++ b/Lib/sets.py
@@ -53,7 +53,7 @@
# and cleaned up the docstrings.
#
# - Raymond Hettinger added a number of speedups and other
-# bugs^H^H^H^Himprovements.
+# improvements.
__all__ = ['BaseSet', 'Set', 'ImmutableSet']
@@ -155,26 +155,35 @@
data[deepcopy(elt, memo)] = value
return result
- # Standard set operations: union, intersection, both differences
+ # Standard set operations: union, intersection, both differences.
+ # Each has an operator version (e.g. __or__, invoked with |) and a
+ # method version (e.g. union).
+
+ def __or__(self, other):
+ """Return the union of two sets as a new set.
+
+ (I.e. all elements that are in either set.)
+ """
+ if not isinstance(other, BaseSet):
+ return NotImplemented
+ result = self.__class__(self._data)
+ result._data.update(other._data)
+ return result
def union(self, other):
"""Return the union of two sets as a new set.
(I.e. all elements that are in either set.)
"""
- self._binary_sanity_check(other)
- result = self.__class__(self._data)
- result._data.update(other._data)
- return result
+ return self | other
- __or__ = union
-
- def intersection(self, other):
+ def __and__(self, other):
"""Return the intersection of two sets as a new set.
(I.e. all elements that are in both sets.)
"""
- self._binary_sanity_check(other)
+ if not isinstance(other, BaseSet):
+ return NotImplemented
if len(self) <= len(other):
little, big = self, other
else:
@@ -187,14 +196,20 @@
data[elt] = value
return result
- __and__ = intersection
+ def intersection(self, other):
+ """Return the intersection of two sets as a new set.
- def symmetric_difference(self, other):
+ (I.e. all elements that are in both sets.)
+ """
+ return self & other
+
+ def __xor__(self, other):
"""Return the symmetric difference of two sets as a new set.
(I.e. all elements that are in exactly one of the sets.)
"""
- self._binary_sanity_check(other)
+ if not isinstance(other, BaseSet):
+ return NotImplemented
result = self.__class__([])
data = result._data
value = True
@@ -206,14 +221,20 @@
data[elt] = value
return result
- __xor__ = symmetric_difference
+ def symmetric_difference(self, other):
+ """Return the symmetric difference of two sets as a new set.
- def difference(self, other):
+ (I.e. all elements that are in exactly one of the sets.)
+ """
+ return self ^ other
+
+ def __sub__(self, other):
"""Return the difference of two sets as a new Set.
(I.e. all elements that are in this set and not in the other.)
"""
- self._binary_sanity_check(other)
+ if not isinstance(other, BaseSet):
+ return NotImplemented
result = self.__class__([])
data = result._data
value = True
@@ -222,7 +243,12 @@
data[elt] = value
return result
- __sub__ = difference
+ def difference(self, other):
+ """Return the difference of two sets as a new Set.
+
+ (I.e. all elements that are in this set and not in the other.)
+ """
+ return self - other
# Membership test