What's The Best Way To Create Exchangeable Tuple Keys For The Same Dictionary Value?

def check(): dict_choice_a = {(a, b) : value, (b, a) : value} #(a, b) and (b, a) refer to the same value but repeted dict_choice_b = {tuple(sorted((a, b)) : value} #not r

Solution 1:

Per the comments, you can put a and b into a frozenset, which is unordered:

dict_choice = {frozenset((a, b)): value}

---

If you need this to be automatic, you could create your own MutableMapping:

classMyDict(MutableMapping):

    def__init__(self, arg=None):
        self._map = {}
        if arg isnotNone:
            self.update(arg)

    def__getitem__(self, key):
        return self._map[frozenset(key)]

    def__setitem__(self, key, value):
        self._map[frozenset(key)] = value

    def__delitem__(self, key):
        del self._map[frozenset(key)]

    def__iter__(self):
        returniter(self._map)

    def__len__(self):
        returnlen(self._map)

In use:

>>>d = MyDict([((1, 2), 'hello'), ((3, 4), 'world')])>>>d[(2, 1)]
'hello' 

However note that this could have unexpected behaviour with other kinds of keys:

>>> d['hello'] = 'world'>>> d['hole']
'world'>>> d[1] = 2
Traceback (most recent call last):
  File "python", line 1, in <module>
  File "python", line 14, in __setitem__
TypeError: 'int'objectisnot iterable

Solution 2:

Using @jonrsharpe solution, I created an alternative for the unexpected behavior with other kinds of keys, considered that only tuples will be used in an unordered way:

classMyDict(MutableMapping):

    def__init__(self, arg=None):
        self._map = {}
        if arg isnotNone:
            self.update(arg)

    def__getitem__(self, key):
        ifisinstance(key, tuple):
            return self._map[frozenset(key)]
        return self._map[key]

    def__setitem__(self, key, value):
        ifisinstance(key, tuple):
            self._map[frozenset(key)] = value
        else:
            self._map[key] = value

    def__delitem__(self, key):
        ifisinstance(key, tuple):
            del self._map[frozenset(key)]
        else:
            del self.map[key]

    def__iter__(self):
        returniter(self._map)

    def__len__(self):
        returnlen(self._map)

    def__str__(self):
        returnstr(self._map)