TypeError unhashable type dict

Question

This piece of code is giving me an error unhashable type  dict can anyone explain me what is the solution      negids   movie reviews fileids  neg   def word feats words       return dict   word  True  for word in words    negfeats     word feats movie reviews words fileids  f      neg   for f in negids  stopset   set stopwords words  english     def stopword filtered word feats words       return dict   word  True  for word in words if word not in stopset    result stopword filtered word feats negfeats

User · Answer

A possible solution might be to use the JSON dumps() method, so you can convert the dictionary to a string ---

import json

a={"a":10, "b":20}
b={"b":20, "a":10}
c = [json.dumps(a), json.dumps(b)]


set(c)
json.dumps(a) in c

Output -

set(['{"a": 10, "b": 20}'])
True

User · Answer

You re trying to use a dict as a key to another dict or in a set  That does not work because the keys have to be hashable  As a general rule  only immutable objects  strings  integers  floats  frozensets  tuples of immutables  are hashable  though exceptions are possible   So this does not work    gt  gt  gt  dict key     a    b    gt  gt  gt  some dict dict key    True Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unhashable type   dict    To use a dict as a key you need to turn it into something that may be hashed first  If the dict you wish to use as key consists of only immutable values  you can create a hashable representation of it like this    gt  gt  gt  key   frozenset dict key items      Now you may use key as a key in a dict or set    gt  gt  gt  some dict key    True  gt  gt  gt  some dict  frozenset    a    b      True    Of course you need to repeat the exercise whenever you want to look up something using a dict    gt  gt  gt  some dict dict key                        Doesn t work Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unhashable type   dict   gt  gt  gt  some dict frozenset dict key items        Works True   If the dict you wish to use as key has values that are themselves dicts and or lists  you need to recursively  freeze  the prospective key  Here s a starting point   def freeze d       if isinstance d  dict           return frozenset  key  freeze value   for key  value in d items        elif isinstance d  list           return tuple freeze value  for value in d      return d

[python] TypeError: unhashable type: 'dict'

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