Replace words in a string using dictionary in Python

In this article, we will discuss how to replace multiple words in a string based on a dictionary.

Table of Contents

Suppose we have a string,

"This is the last rain of Season and Jack is here."

We want to replace multiple words in this string using a dictionary i.e.

{'is' : 'AA',
 'the': 'BBB',
 'and': 'CCC'}

Keys in the dictionary are the substrings that need to be replaced, and the corresponding values in the dictionary are the replacement strings. Like, in this case,

• “is” should be replaced by “AA”
• “the” should be replaced by “BBB”
• “and” should be replaced by “CCC”

The final string should be like,

ThAA AA BBB last rain of Season CCC Jack AA here.

There are different ways to do this. Let’s discuss them one by one.

Using str.replace() function

The string class has a member function replace(to_be_replaced, replacement) and it replaces all the occurrences of substring “to_be_replaced” with “replacement” string.

To replace all the multiple words in a string based on a dictionary. We can iterate over all the key-value pairs in a dictionary and, for each pair, replace all the occurrences of “key” substring with “value” substring in the original string.

For example:

strValue = "This is the last rain of Season and Jack is here."

# Dictionary containing mapping of 
# values to be replaced and replacement values
dictOfStrings = {'is' : 'AA',
                 'the': 'BBB',
                 'and': 'CCC'}

# Iterate over all key-value pairs in dict and 
# replace each key by the value in the string
for word, replacement in dictOfStrings.items():
    strValue = strValue.replace(word, replacement)

print(strValue)

Output:

ThAA AA BBB last rain of Season CCC Jack AA here.

It replaced all the dictionary keys/words in a string with the corresponding values from the dictionary.

Using Regex

In Python, the regex module provides a function sub(pattern, replacement_str, original_str) to replace the contents of a string based on a matching regex pattern.

This function returns a modified copy of given string “original_str” after replacing all the substrings that matches the given regex “pattern” with a substring “replacement_str”.

To replace all the multiple substrings in a string based on a dictionary. We can loop over all the key-value pairs in a dictionary and for each key-value pair, replace all the occurrences of “key” substring with “value” substring in the original string using the regex.sub() function.

For example:

import re

strValue = "This is the last rain of Season and Jack is here."

# Dictionary containing mapping of 
# values to be replaced and replacement values
dictOfStrings = {'is' : 'AA',
                 'the': 'BBB',
                 'and': 'CCC'}

# Iterate over all key-value pairs in dict and 
# replace each key by the value in the string
for word, replacement in dictOfStrings.items():
    strValue = re.sub(word, replacement, strValue)


print(strValue)

Output:

ThAA AA BBB last rain of Season CCC Jack AA here.

It replaced all the dictionary keys/words in a string with the corresponding values from the dictionary.

Summary:

We learned to replace multiple words in a string based on a dictionary in Python.