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Python Python Collections (Retired) Dictionaries Word Count

Zachary Vacek
Zachary Vacek
11,133 Points
Posted by Zachary Vacek
Zachary Vacek
11,133 Points

Counting words in a string using a dictionary - Python Collection Challenge

def word_count(string):
  my_string = string.lower().split()
  my_dict = {}
  for item in my_string:
    my_dict[item] = item.count(item)
  print(my_dict)

word_count("I am that I am")

The program is running without any errors, but I can't figure out why it isn't properly counting the items in the string.

It should be printing {'i': 2, 'am': 2, 'that': 1}

but it's printing {'i': 1, 'am': 1, 'that': 1}

Can someone help me figure out why this may be?

Thanks!

  • Zac
word_count.py 
# 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.

3 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

What your original code was doing, as you figured out, was reassigning the dictionary value each time an item was seen effective only counting the last time it was seen. Also, item.count(item) will always return 1 on any string.

In your updated solution, you are effectively recounting an item many times, overriding the value with the last time an item was seen. This parses the full string for each item present. As the string gets longer this becomes much more inefficient. To count the string in a single pass, keep track if the item is first seen or should increment by 1:

def word_count(string):
    my_string = string.lower().split()
    my_dict = {}
    for item in my_string:
        if item in my_dict:
            my_dict[item] += 1
        else:
            my_dict[item] = 1
    print(my_dict)
Zachary Vacek
Zachary Vacek
11,133 Points
Zachary Vacek
Zachary Vacek
11,133 Points

Got it!

def word_count(string):
  my_string = string.lower().split()
  my_dict = {}
  for item in my_string:
    my_dict[item] = my_string.count(item)
  print(my_dict)

word_count("I am that I am.")
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

I promoted this to an answer, but then saw this is a hidden error in the code. See my answer.

Ali Katkar
Ali Katkar
768 Points
Ali Katkar
Ali Katkar
768 Points 
wordCounts = {}
for word in string.lower().split():
    count = wordCounts.get(word, 0)
    wordCounts[word] = count + 1

or simply

words =  string.lower().split()
wordCounts = { word: words.count(word) for word in words }