A Concise Introduction to Programming in Python

Chapter 18

Dictionaries

Imagine writing a program that counts the number of times each word appears

in a large file. We could store the counts in a list, but then how do we keep

track of which word uses which index? We could store the words in a separate

second list, so that the count for the word in words[i] is in counts[i], but

then we would have to search the entire word list every time we came to

another word to count. A dictionary is much more efficient.

Listing 18.1: Word Frequency

1 # wordfreq.py

2

3 import string

4

5 def getwords(fname):

6 with open(fname) as f:

7 s = f.read().lower()

8 s = s.translate(s.maketrans("", "", string.punctuation))

9 return