Adventures in Machine Learning

Efficiently Replace Words in a String Using Python’s Dictionary and resub() Method

Have you ever found yourself in a situation where you need to replace certain words in a string with other words in a quick and efficient manner? Perhaps you have a long piece of text where certain words were used incorrectly, or you need to replace a set of words with their synonyms.

Fear not, there are two methods you can use to make this task simpler and easier – by replacing words using a dictionary or by using the re.sub() method.

Replacing Words in a String using a Dictionary

The method of replacing words in a string using a dictionary is a powerful and straightforward way to update your text. Suppose you have a string that needs to be modified to correct spelling errors or replace obsolete information.

You can create a dictionary of words that need to be replaced and their corresponding replacements and then use the str.replace() method to replace the words in the string. For example, suppose you have a sentence: “The cAt is playing with a ball.” You want to replace the word “cAt” with “cat” and “ball” with “toy”.

Firstly, you would need to create a dictionary of words with their replacements, like this:

word_dict = {‘cAt’: ‘cat’, ‘ball’: ‘toy’}

Then you can use the str.replace() method to replace all instances of the words in the dictionary. Here’s how you do it:

sentence = “The cAt is playing with a ball.”

for word in word_dict:

sentence = sentence.replace(word, word_dict[word])


The output of this code would be: “The cat is playing with a toy.”

This method can also be used to convert words to lowercase. You can assign all your keys or values to lowercase, so that any instances of them that appear in the string are also assigned to lowercase.

For example:

word_dict = {‘cAt’: ‘cat’, ‘BALL’: ‘toy’}

word_dict = {key.lower():value.lower() for key, value in word_dict.items()}

Using this updated dictionary, the program would replace all instances of “cAt” and “BALL” in the string and replace them with “cat” and “toy,” respectively, regardless of their original capitalization. Using re.sub() to Replace Words in a String with a dictionary

The second method to replace words in a string using a dictionary is by using the re.sub() method.

This method is particularly useful if you’re working with a large text file or multiple files at once since it has the potential to automate a bulk edit process. This method involves creating a regular expression pattern and using it to replace words in the string.

You can create a function that takes a dictionary of words to be replaced and their corresponding replacements and returns a regex pattern that matches the words to be replaced. You can then use this pattern in the re.sub() method to replace the words in the string.

Here’s an example of how to use this method:

import re

def replace_words_in_string(word_dict, string):

pattern = r’b(‘ + ‘|’.join(word_dict.keys()) + r’)b’

regex = re.compile(pattern, re.IGNORECASE)

return regex.sub(lambda x: word_dict[], string)

word_dict = {‘cAt’: ‘cat’, ‘BALL’: ‘toy’}

string = “The cAt is playing with a ball.”

modified_string = replace_words_in_string(word_dict, string)


The output of this code would be: “The cat is playing with a toy.”

Notice that this code has an added feature that enables us to replace words in a case-insensitive manner. The second argument to re.compile() is the re.IGNORECASE flag, which tells the method to ignore the case when matching the pattern in the string.


In conclusion, these two methods of replacing words in a string using a dictionary or re.sub() are incredibly useful for modifying text efficiently. By creating a dictionary of words and their replacements or a regular expression pattern, you can modify the text in a quick and efficient manner.

These methods can help improve written works such as articles, student papers, or documents. Hopefully, this article has given you some useful insights into how you can modify your text.

Go ahead and try these methods out on some of your own texts today!

Are you interested in learning more about replacing words in a string using a dictionary or using re.sub() method? Fortunately, there are a variety of online tutorials and resources available to help you dive deeper into these topics and gain additional knowledge and skills.

Here are some useful resources that can help you:

1. Python documentation

The official Python documentation provides comprehensive information about string methods, regular expressions, and other relevant topics that can help you to work with text data in Python.

The documentation features examples and explanations that make it easy for you to understand how to use these Python functions and modules correctly. Whether you are a beginner or advanced programmer, the documentation provides useful insights and examples relevant to the task at hand.

2. Real Python

Real Python is a platform that offers a wide range of Python tutorials and guides.

It is an excellent source for comprehensive tutorials on Python programming. Whether you’re an experienced programmer looking for advanced tutorials or a beginner looking to learn the basics, Real Python offers a variety of articles, courses, and videos to address your needs and skill level.

Real Python also features various articles on working with text data in Python, including using regular expressions and string methods, like replace(). The tutorials feature hands-on examples to help you make sense of the concepts presented.

3. Codecademy

Codecademy is an online learning platform that offers coding classes and a wide range of programming tutorials, including Python.

The courses available at Codecademy are often interactive, featuring exercises and projects for you to work on, allowing you to apply the skills you learn as you go. Codecademy provides a hands-on approach to the learning process.

Their Python course includes tutorials on string manipulation and regular expressions that will allow you to take a deep dive into the topic. The syllabus and the exercises are quite comprehensive, and you can go at your own pace, which makes learning easier.

4. Stack Overflow

Stack Overflow is a valuable resource for programmers.

It’s a question-and-answer site that allows programmers to ask and answer questions related to programming and software development. If you have a particular question related to the methods or concepts described above, you can search for it on Stack Overflow and receive answers from other programmers in the community.

With time, Stack Overflow has become a vast storehouse of knowledge and a go-to resource for software developers, and as a result, any programmer interested in text data manipulation techniques will find the platform valuable. 5.

YouTube Tutorials

If you are someone who learns better through video tutorials, YouTube is a great resource for Python. There are a variety of channels and videos that cater to different skill levels, learning styles, and preferences that cover various Python modules or concepts.

Some useful channels that cover data manipulation topics include Corey Schafer, sentdex, and Tech With Tim. These channels provide step-by-step tutorials that come with useful examples in applicable projects.

Watching videos on YouTube may be a more engaging way to learn how to replace words in a string or work with regular expressions, so it is worth checking out.


In conclusion, there are plenty of resources both online and offline to help you improve your knowledge and skills in text data manipulation. If you’re interested in learning about replacing words in a string using a dictionary or using re.sub() method, the resources covered here are a great place to start.

By making use of the resources mentioned in this article, you will be able to learn and get started with text data manipulation easily and efficiently. In summary, this article has explained two methods to replace words in a string using a dictionary or using the re.sub() method.

The former method is useful when making straightforward replacements, while the latter is more suitable for large text files or multiple files. The article has provided insights into additional resources that offer relevant tutorials on these topics, which are useful for learners with varying needs.

These methods are essential in making quick and efficient updates to text data and can help improve written works like articles, student papers, and other documents. By utilizing these methods and resources, you can develop the necessary skills to manipulate text data in Python.

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