Python – Replace words from Dictionary

Last Updated : 10 Jan, 2025

Replacing words in a string using a dictionary allows us to efficiently map specific words to new values.

Using `str.replace()` in a Loop

Using str.replace() in a loop, you can systematically replace specific substrings within a string with new values. This approach is useful for repetitive replacements, such as modifying multiple words or characters.

Python

# Input string s = "hello world, have a great day"  # Dictionary of words to replace r_dict = {"hello": "hi", "world": "earth", "great": "wonderful"}  # Replace words in the string using a loop for o_word, n_word in r_dict.items():     s = s.replace(o_word, n_word)  # Print the result print(s)

Output

hi earth, have a wonderful day

Explanation

r_dict dictionary defines the words to replace as keys and their corresponding new words as values. By iterating through the dictionary, each key-value pair is used to replace occurrences in the input string.
str.replace() method is applied in each iteration to replace the old word (o_word) with the new word (n_word).

Let’s understand various other methods to Replace words from Dictionary

Table of Content

Using Regular Expressions (`re.sub()`)

This method uses re.sub() with a dynamically created regex pattern to find all target words in the string. A lambda function is used for on-the-fly substitution, replacing each matched word with its corresponding value from the dictionary.

Python

import re  # Input string s = "hello world, have a great day"  # Dictionary of words to replace r_dict = {"hello": "hi", "world": "earth", "great": "wonderful"}  # Replace words using re.sub with a function result = re.sub(r'\b(?:' + '|'.join(r_dict.keys()) + r')\b',                 lambda match: r_dict[match.group()], s)  # Print the result print(result)

Output

hi earth, have a wonderful day

Explanation

The code constructs a regex pattern dynamically to match whole words from the dictionary keys using re.sub().
A lambda function is used to replace each matched word with its corresponding value from the dictionary

Using List Comprehension

Using list comprehension provides a concise and efficient way to replace words in a string. By iterating through each word, it checks if the word exists in a dictionary and replaces it, otherwise keeping the original word.

Python

# Input string s = "hello world, have a great day"  # Dictionary of words to replace r_dict = {"hello": "hi", "world": "earth", "great": "wonderful"}  # Replace words using list comprehension and join result = ' '.join([r_dict.get(word, word) for word in s.split()])  # Print the result print(result)

Output

hi world, have a wonderful day

Explanation

The string is split into words, and list comprehension iterates through each word.
For each word, it checks if it’s in the dictionary r_dict. If it is, it replaces it; otherwise, the original word remains.
The words are then joined back into a string using ' '.join() and printed.

Using `str.split()` and `map()`

str.split() method divides the string into words, and map() applies a replacement function to each word using the dictionary. Finally, the modified words are joined back into a string.

Python

s = "hello world, have a great day"  # Dictionary of words to replace r_dict = {"hello": "hi", "world": "earth", "great": "wonderful"}  # Replace words using split and map result = ' '.join(map(lambda word: r_dict.get(word, word), s.split()))  # Print the result print(result)

Output

hi world, have a wonderful day

Explanation

The str.split() method breaks the string into words, and map() applies a function to replace each word using the dictionary.
The lambda function checks if the word exists in the dictionary; if it does, it replaces it, otherwise, it keeps the original word.

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Python – Replace words from Dictionary

Using str.replace() in a Loop

Using Regular Expressions (re.sub())

Using List Comprehension

Using str.split() and map()

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Using `str.replace()` in a Loop

Using Regular Expressions (`re.sub()`)

Using `str.split()` and `map()`