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"""Key functions for memoizing decorators."""
__all__ = ("hashkey", "typedkey")
class _HashedTuple(tuple):
"""A tuple that ensures that hash() will be called no more than once
per element, since cache decorators will hash the key multiple
times on a cache miss. See also _HashedSeq in the standard
library functools implementation.
"""
__hashvalue = None
def __hash__(self, hash=tuple.__hash__):
hashvalue = self.__hashvalue
if hashvalue is None:
self.__hashvalue = hashvalue = hash(self)
return hashvalue
def __add__(self, other, add=tuple.__add__):
return _HashedTuple(add(self, other))
def __radd__(self, other, add=tuple.__add__):
return _HashedTuple(add(other, self))
def __getstate__(self):
return {}
# used for separating keyword arguments; we do not use an object
# instance here so identity is preserved when pickling/unpickling
_kwmark = (_HashedTuple,)
def hashkey(*args, **kwargs):
"""Return a cache key for the specified hashable arguments."""
if kwargs:
return _HashedTuple(args + sum(sorted(kwargs.items()), _kwmark))
else:
return _HashedTuple(args)
def typedkey(*args, **kwargs):
"""Return a typed cache key for the specified hashable arguments."""
key = hashkey(*args, **kwargs)
key += tuple(type(v) for v in args)
key += tuple(type(v) for _, v in sorted(kwargs.items()))
return key
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