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"""Misc dict tools."""
__all__ = ["hashdict"]
# https://stackoverflow.com/questions/1151658/python-hashable-dicts
class hashdict(dict):
"""
hashable dict implementation, suitable for use as a key into
other dicts.
>>> h1 = hashdict({"apples": 1, "bananas":2})
>>> h2 = hashdict({"bananas": 3, "mangoes": 5})
>>> h1+h2
hashdict(apples=1, bananas=3, mangoes=5)
>>> d1 = {}
>>> d1[h1] = "salad"
>>> d1[h1]
'salad'
>>> d1[h2]
Traceback (most recent call last):
...
KeyError: hashdict(bananas=3, mangoes=5)
based on answers from
http://stackoverflow.com/questions/1151658/python-hashable-dicts
"""
def __key(self):
return tuple(sorted(self.items()))
def __repr__(self):
return "{0}({1})".format(
self.__class__.__name__,
", ".join("{0}={1}".format(str(i[0]), repr(i[1])) for i in self.__key()),
)
def __hash__(self):
return hash(self.__key())
def __setitem__(self, key, value):
raise TypeError(
"{0} does not support item assignment".format(self.__class__.__name__)
)
def __delitem__(self, key):
raise TypeError(
"{0} does not support item assignment".format(self.__class__.__name__)
)
def clear(self):
raise TypeError(
"{0} does not support item assignment".format(self.__class__.__name__)
)
def pop(self, *args, **kwargs):
raise TypeError(
"{0} does not support item assignment".format(self.__class__.__name__)
)
def popitem(self, *args, **kwargs):
raise TypeError(
"{0} does not support item assignment".format(self.__class__.__name__)
)
def setdefault(self, *args, **kwargs):
raise TypeError(
"{0} does not support item assignment".format(self.__class__.__name__)
)
def update(self, *args, **kwargs):
raise TypeError(
"{0} does not support item assignment".format(self.__class__.__name__)
)
# update is not ok because it mutates the object
# __add__ is ok because it creates a new object
# while the new object is under construction, it's ok to mutate it
def __add__(self, right):
result = hashdict(self)
dict.update(result, right)
return result
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