Python - Replace words from Dictionary

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.

# 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)

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

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.

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)

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.

# 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)

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.

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)

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.