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#
# A Set class that works all the way back to Python 1.5. From:
#
# Python Cookbook: Yet another Set class for Python
# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/106469
# Goncalo Rodriques
#
# This is a pure Pythonic implementation of a set class. The syntax
# and methods implemented are, for the most part, borrowed from
# PEP 218 by Greg Wilson.
#
# Note that this class violates the formal definition of a set() by adding
# a __getitem__() method so we can iterate over a set's elements under
# Python 1.5 and 2.1, which don't support __iter__() and iterator types.
#
import string
class Set:
"""The set class. It can contain mutable objects."""
def __init__(self, seq = None):
"""The constructor. It can take any object giving an iterator as an optional
argument to populate the new set."""
self.elems = []
if seq:
for elem in seq:
if elem not in self.elems:
hash(elem)
self.elems.append(elem)
def __str__(self):
return "set([%s])" % string.join(map(str, self.elems), ", ")
def copy(self):
"""Shallow copy of a set object."""
return Set(self.elems)
def __contains__(self, elem):
return elem in self.elems
def __len__(self):
return len(self.elems)
def __getitem__(self, index):
# Added so that Python 1.5 can iterate over the elements.
# The cookbook recipe's author didn't like this because there
# really isn't any order in a set object, but this is necessary
# to make the class work well enough for our purposes.
return self.elems[index]
def items(self):
"""Returns a list of the elements in the set."""
return self.elems
def add(self, elem):
"""Add one element to the set."""
if elem not in self.elems:
hash(elem)
self.elems.append(elem)
def remove(self, elem):
"""Remove an element from the set. Return an error if elem is not in the set."""
try:
self.elems.remove(elem)
except ValueError:
raise LookupError, "Object %s is not a member of the set." % str(elem)
def discard(self, elem):
"""Remove an element from the set. Do nothing if elem is not in the set."""
try:
self.elems.remove(elem)
except ValueError:
pass
def sort(self, func=cmp):
self.elems.sort(func)
#Define an iterator for a set.
def __iter__(self):
return iter(self.elems)
#The basic binary operations with sets.
def __or__(self, other):
"""Union of two sets."""
ret = self.copy()
for elem in other.elems:
if elem not in ret:
ret.elems.append(elem)
return ret
def __sub__(self, other):
"""Difference of two sets."""
ret = self.copy()
for elem in other.elems:
ret.discard(elem)
return ret
def __and__(self, other):
"""Intersection of two sets."""
ret = Set()
for elem in self.elems:
if elem in other.elems:
ret.elems.append(elem)
return ret
def __add__(self, other):
"""Symmetric difference of two sets."""
ret = Set()
temp = other.copy()
for elem in self.elems:
if elem in temp.elems:
temp.elems.remove(elem)
else:
ret.elems.append(elem)
#Add remaining elements.
for elem in temp.elems:
ret.elems.append(elem)
return ret
def __mul__(self, other):
"""Cartesian product of two sets."""
ret = Set()
for elemself in self.elems:
x = map(lambda other, s=elemself: (s, other), other.elems)
ret.elems.extend(x)
return ret
#Some of the binary comparisons.
def __lt__(self, other):
"""Returns 1 if the lhs set is contained but not equal to the rhs set."""
if len(self.elems) < len(other.elems):
temp = other.copy()
for elem in self.elems:
if elem in temp.elems:
temp.remove(elem)
else:
return 0
return len(temp.elems) == 0
else:
return 0
def __le__(self, other):
"""Returns 1 if the lhs set is contained in the rhs set."""
if len(self.elems) <= len(other.elems):
ret = 1
for elem in self.elems:
if elem not in other.elems:
ret = 0
break
return ret
else:
return 0
def __eq__(self, other):
"""Returns 1 if the sets are equal."""
if len(self.elems) != len(other.elems):
return 0
else:
return len(self - other) == 0
def __cmp__(self, other):
"""Returns 1 if the sets are equal."""
if self.__lt__(other):
return -1
elif other.__lt__(self):
return 1
else:
return 0
# Local Variables:
# tab-width:4
# indent-tabs-mode:nil
# End:
# vim: set expandtab tabstop=4 shiftwidth=4:
|
