Python Regex: re.search() VS re.findall()

Python’s re module provides powerful tools to search, match and manipulate text using regular expressions. Two commonly used functions are re.search(), which finds the first occurrence of a pattern in a string and re.findall(), which retrieves all matches of a pattern throughout the string. Understanding how each works will help you effectively handle text processing tasks.

What is re.search() ?

re.search() function scans through a string, looking for the first location where the regular expression pattern produces a match. It returns a match object if a match is found, otherwise returns None.

Example:

import re
s = "My favorite fruits are apple, banana, and mango."
res = re.search(r'\b\w*a\b', s)

if res:
    print(res.group())
else:
    print("Not found.")

banana

Explanation:

• re.search(r'\b\w*a\b', s) looks for the first word in the string that ends with the letter 'a'.
• pattern \b\w*a\b means the word must start and end at a word boundary (\b), contain any number of word characters (\w*) and end specifically with 'a'.

What is re.findall() ?

re.findall() function returns all non-overlapping matches of a pattern in a string as a list of strings. If the pattern has capturing groups, it returns a list of tuples.

import re
s = "My favorite fruits are apple, banana, and mango."

res = re.findall(r'\b\w*a\b', s)
print(res)

['banana']

Explanation:

• re.findall(r'\b\w*a\b', s) finds all words in the string that end with the letter 'a'.
• pattern \b\w*a\b means the word must start and end at a word boundary (\b), contain any number of word characters (\w*) and end specifically with 'a'.

Example with capturing Groups

Capturing groups in regular expressions are used to extract specific parts of the matched text. You create a group by placing part of the pattern inside parentheses ().

Example 1: In this example, we want to extract the price (just the number) after the word Price by using re.search().

import re

s = "Price: $30, Discount: $5"
res = re.search(r'Price: \$(\d+)', s)
if res:
    print(res.group(1))

30

Explanation:

• re.search(r'Price: \$(\d+)', s) looks for the first occurrence of the word "Price:" followed by a dollar sign $ and then one or more digits.
• pattern Price: \$(\d+) uses parentheses () to create a capturing group that extracts just the number after "Price: $".

Example 2: Now, suppose you want to extract all numbers that come after a dollar sign ($) in the sentence. You can use re.findall() for this.

import re
s = "Price: $30, Discount: $5"

res = re.findall(r'\$(\d+)', s)
print(res)

['30', '5']

Explanation:

• re.findall(r'\$(\d+)', s) searches the entire string for all numbers that come after a dollar sign $.
• pattern \$(\d+) uses a capturing group (\d+) to extract one or more digits following each $ symbol.

Difference between research() and re.findall()

Both functions are used to find patterns in text, but they serve different purposes depending on whether you need a single match or all matches. The table below highlights the key differences to help you choose the right function for your task.