How Can I Find All Matches to a Regular Expression in Python?

In Python, regular expressions (regex) are a powerful tool for finding patterns in text. Whether we're searching through logs, extracting specific data from a document, or performing complex string manipulations, Python's re module makes working with regular expressions straightforward.

In this article, we will learn, how we can find all matches of a a regular expression.

The Re Module

Python's re module is the built-in library that provides support for regular expressions. It includes functions for compiling regular expressions, searching strings, and retrieving matches. Before using any regex functions, we need to import the re module.

import re

Finding Matches

There are a number of ways by which we can find matches in Python using Regular Expression module. Let us see them one by one.

The re.findall() Function

One of the most common ways to find all matches in Python is by using the re.findall( ) function. This function returns a list of all non-overlapping matches of the pattern in the string.

The re.findall() function takes two main arguments. The first is the regex pattern you want to search for and the string where you want to perform the search. It then returns a list of all matches found. If no matches are found, it returns an empty list.

Example:

In this example, we will import the re module and a sample string. Then we will use the findall() function to find the words that ends with a certain word. The \b denotes a word boundary, ensuring that the match is at the end of a word.

import re

text = "The rain in Spain falls mainly in the plain."

# Find all words that end with 'ain'
matches = re.findall(r'\b\w*ain\b', text)

print(matches)

Output:

['rain', 'Spain', 'plain']

The re.finditer() Function

The re.findall() returns a list of matches, re.finditer() returns an iterator yielding match objects. This is particularly useful when you need more information about each match, such as its position within the string.

Example:

In this example, the regex pattern r'\$\d+\.\d{2}' matches dollar amounts (e.g., "$5.00"). The match.group() method retrieves the matched text, and match.span() returns the start and end positions of each match.

import re

text = "The price is $5.00, and the discount is $1.50."

# Find all currency amounts
matches = re.finditer(r'\$\d+\.\d{2}', text)

for match in matches:
    print(f"Match: {match.group()} at position {match.span()}")

Output:

Match: $5.00 at position (13, 18)
Match: $1.50 at position (40, 45)

Using Capture Groups

If our regex contains capture groups (i.e., patterns enclosed in parentheses), re.findall() will return tuples containing the captured groups. This allows us to extract specific parts of each match.

Example:

Here, the pattern ([\w\.-]+)@([\w\.-]+) captures the username and domain name separately. The first group matches the username, and the second group matches the domain.

import re

text = "gfg's email is [email protected], \
		and Jane's email is [email protected]."

# Extract all usernames and domain names from the emails
matches = re.findall(r'([\w\.-]+)@([\w\.-]+)', text)

print(matches)

Output:

[('gfg.doe', 'example.com'), ('geeks_doe123', 'work.net')]

Conclusion

When working with regular expressions in Python, we can easily find all matches using re.findall() for simple patterns or re.finditer() if you need more detailed match information. These functions are versatile and can handle a wide range of use cases, making them essential tools for text processing tasks. Understanding and mastering regex can greatly enhance your ability to manipulate and analyze text data in Python, whether it’s for simple searches or complex string parsing.