How to overcome TypeError: unhashable type: 'list'

As indicated by the other answers, the error is to due to k = list[0:j], where your key is converted to a list. One thing you could try is reworking your code to take advantage of the split function:

# Using with ensures that the file is properly closed when you're done
with open('filename.txt', 'rb') as f:
  d = {}
  # Here we use readlines() to split the file into a list where each element is a line
  for line in f.readlines():
    # Now we split the file on `x`, since the part before the x will be
    # the key and the part after the value
    line = line.split('x')
    # Take the line parts and strip out the spaces, assigning them to the variables
    # Once you get a bit more comfortable, this works as well:
    # key, value = [x.strip() for x in line] 
    key = line[0].strip()
    value = line[1].strip()
    # Now we check if the dictionary contains the key; if so, append the new value,
    # and if not, make a new list that contains the current value
    # (For future reference, this is a great place for a defaultdict :)
    if key in d:
      d[key].append(value)
    else:
      d[key] = [value]

print d
# {'AAA': ['111', '112'], 'AAC': ['123'], 'AAB': ['111']}

Note that if you are using Python 3.x, you'll have to make a minor adjustment to get it work properly. If you open the file with rb, you'll need to use line = line.split(b'x') (which makes sure you are splitting the byte with the proper type of string). You can also open the file using with open('filename.txt', 'rU') as f: (or even with open('filename.txt', 'r') as f:) and it should work fine.

Note: This answer does not explicitly answer the asked question. the other answers do it. Since the question is specific to a scenario and the raised exception is general, This answer points to the general case.

Hash values are just integers which are used to compare dictionary keys during a dictionary lookup quickly.

Internally, hash() method calls __hash__() method of an object which are set by default for any object.

Converting a nested list to a set

>>> a = [1,2,3,4,[5,6,7],8,9]
>>> set(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

This happens because of the list inside a list which is a list which cannot be hashed. Which can be solved by converting the internal nested lists to a tuple,

>>> set([1, 2, 3, 4, (5, 6, 7), 8, 9])
set([1, 2, 3, 4, 8, 9, (5, 6, 7)])

Explicitly hashing a nested list

>>> hash([1, 2, 3, [4, 5,], 6, 7])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'


>>> hash(tuple([1, 2, 3, [4, 5,], 6, 7]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

>>> hash(tuple([1, 2, 3, tuple([4, 5,]), 6, 7]))
-7943504827826258506

The solution to avoid this error is to restructure the list to have nested tuples instead of lists.