How do I fix TypeError: unhashable type: 'list' Error

Question

I've been searching in other questions, but I found no help. I got this code:

def pairs(self, listOrString):
        if listOrString:
            return filter(re.compile(self.pairwise(self.text)).match, frozenset(self.text))
        else:
            return ' '.join(filter(re.compile(self.pairwise(self.text)).match, frozenset(self.text)))

def pairs_freqency(self):
    return Counter(self.pairs(True))

def sum_pairs(self):
        return len(self.ngrams(self.letters(list),2))

def pair_probability(self):
{pair : freqency / self.sum_pairs() for (pair, freqency) in self.pairs_freqency().iteritems()}

def pairwise(self, sequence):
    x,y = tee(sequence)
    next(y)
    return zip(x,y)

But when I try to print:

print pairs_freqency()

I get this error:

**Updated

     Traceback (most recent call last):
  File "...", line 281, in <module>
    print pairs(string, text)
  File "...", line 46, in get_pairs
    return filter(re.compile(self.pairwise(self.text)).match, frozenset(self.text))
  File "...", line 190, in compile
    return _compile(pattern, flags)
  File "...", line 232, in _compile
    p = _cache.get(cachekey)
TypeError: unhashable type: 'list'

Can someone help me as fast as possible.
Thanks.

Answer 1

TypeError: unhashable type: 'list' Error happens when you try to use a list as key in a dict (or member of set or frozenset). The standard way to solve this issue is to cast a list to tuple, for example:

In [4]: my_dict = {[2,3,4] : 'a'}
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-cda6d34218c4> in <module>()
----> 1 my_dict = {[2,3,4] : 'a'}

TypeError: unhashable type: 'list'

In [5]: my_dict = {tuple([2,3,4]) : 'a'}
In [6]: my_dict
Out[6]: {(2, 3, 4): 'a'}

Answer 2

Counter needs as its argument an iterable each of whose items is hashable (==can be a key into a dict). The items in you cases are lists, which are not hashable (because they're mutable). Fix: use tuples instead, specifically in your pairs method -- instead of

    return filter(re.compile(self.pairwise(self.text)).match, list(self.text))

use

    return filter(re.compile(self.pairwise(self.text)).match, tuple(self.text))