class _CaptureEq:
'Object wrapper that remembers "other" for successful equality tests.'
def __init__(self, obj):
self.obj = obj
self.match = obj
def __eq__(self, other):
result = (self.obj == other)
if result:
self.match = other
return result
def __getattr__(self, name): # support hash() or anything else needed by __contains__
return getattr(self.obj, name)
def get_equivalent(container, item, default=None):
'''Gets the specific container element matched by: "item in container".
Useful for retreiving a canonical value equivalent to "item". For example, a
caching or interning application may require fetching a single representative
instance from many possible equivalent instances).
>>> get_equivalent(set([1, 2, 3]), 2.0) # 2.0 is equivalent to 2
2
>>> get_equivalent([1, 2, 3], 4, default=0)
0
'''
t = _CaptureEq(item)
if t in container:
return t.match
return default
import doctest
print doctest.testmod()
