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.

Solution 1

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))

Solution 2

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'}

Comments

[Toni]

I don't understand that, can u give me an example?

[Malik Brahimi]

I can't follow your traceback but if you can find the list put frozenset() around it.

[SethMMorton]

Isn't a tuple a better hashable replacement for a list than a frozenset?

[Malik Brahimi]

Perhaps, it is simply a preference.

[Malik Brahimi]

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

[Alex Martelli]

@Borgmester I see the error is actually in re.compile(self.pairwise(self.text)) -- it doesn't actually get to the point where my (still-needed) fix will help. So show us what self.pairwise(self.txt) returns (and the code for that pairwise), which you have not shown so far (do so editing your Q, it's not readable in comments).

[Alex Martelli]

@Borgmester, if self.text was a string, the error from re.compile would be TypeError: first argument must be string or compiled pattern. So what is self.text instead? In any case pairwise returns a zip result (a list, as it happens, but a tuple would be no better) and that can never be the right type of argument for re.compile. So what is self.text, and what did you think re.compileing that zip would do?!