Word frequency counter in Python

To count words, split the text into words and keep a dictionary where each key is a word and each value is how many times you have seen it.

The program

text = "The cat sat on the mat. The cat was happy, and the mat was warm."

counts = {}
for word in text.lower().split():
    word = word.strip(".,!?;:")
    counts[word] = counts.get(word, 0) + 1

for word, n in counts.items():
    print(word, n)

the 4
cat 2
sat 1
on 1
mat 2
was 2
happy 1
and 1
warm 1

How it works

• text.lower() makes "The" and "the" the same word. Without it, they would be counted separately.
• split() with no argument splits on any run of spaces, tabs or new lines.
• word.strip(".,!?;:") removes punctuation from both ends, so "mat." and "mat" are the same word.
• counts.get(word, 0) gives the current count, or 0 if the word is not in the dictionary yet. Then + 1 adds this occurrence.
• A dictionary keeps keys in the order they were first added, so the words print in the order they first appear in the text.

Another way: Counter

collections.Counter does the counting for you, and most_common(n) gives the n most frequent words, largest count first:

from collections import Counter

text = "The cat sat on the mat. The cat was happy, and the mat was warm."
words = [w.strip(".,!?;:") for w in text.lower().split()]

for word, n in Counter(words).most_common(3):
    print(word, n)

the 4
cat 2
mat 2

When two words have the same count, most_common() keeps them in the order they were first seen.