TypeError: 'list' object is not callable /// In ex26 learning Python the hard Way

Here is the output I am receiving, and I am having trouble of what to check for when I re examine my code for the indicated lines.

Traceback (most recent call last):
   File "ex27.py", line 93, in <module>
     print_first_and_last_sorted(sentence)
   File "ex27.py", line 35, in print_first_and_last_sorted
     words = sort_sentence(sentence)
   File "ex27.py", line 25, in sort_sentence
     return sort_words(words)
 

Can anyone shed some light?

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