Why does using a dictionary as a key in a set raise a \'TypeError: unhashable type: \'dict\'\' error?

TypeError: Unhashable Type: 'dict'

Problem:

Why does the following code raise a "TypeError: unhashable type: 'dict'" error?

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)

Answer:

The error occurs because you are attempting to use a dictionary as a key in the set created by the stopset variable. However, dictionaries are not hashable objects, which means they cannot be used as keys in sets or dictionaries.

Solution:

To resolve the issue, you can convert the dictionaries in negfeats to frozen sets, which are hashable. The following code shows the corrected version:

negfeats = [(frozenset(word_feats(movie_reviews.words(fileids=[f])).items()), '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)

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