It says some words are missing

# E.g. word_count("I am that I am") gets back a dictionary like:
# {'i': 2, 'am': 2, 'that': 1}
# Lowercase the string to make it easier.
# Using .split() on the sentence will give you a list of words.
# In a for loop of that list, you'll have a word that you can
# check for inclusion in the dict (with "if word in dict"-style syntax).
# Or add it to the dict with something like word_dict[word] = 1.

a_string = "{i} {will} {be} {great}"

string_dict = a_string.split()

def word_count(a_string):
  string_dict = {}

  for word in a_string.split():
    if word in string_dict:
      string_dict[word] += 1
  else:
      string_dict[word]= 1
  return string_dict