This Python function takes in a list of words (all_words) and a prefix and returns
 a new list of words (words_with_prefix) containing all the words in that list starting
 with the specified prefix.
 """
 def get_words_with_prefix(all_words, prefix):
     words_with_prefix = None
     for word in all_words:
         if word[0:len(prefix) - 1] is prefix:
             words_with_prefix += word
     return words_with_prefix