Python Regex search()

Summary: in this tutorial, you’ll learn how to use the Python regex search() function to return the first match of a pattern in a string.

Introduction to the Python regex search() function

The regex search() is a function in the built-in re module that deals with regular expressions. The search() function has the following syntax:

re.search(pattern, string, flags=0)Code language: Python (python)

In this syntax:

• pattern is a regular expression that you want to search for in the string.
• string is the input string.
• flags is one or more regular expression flags that modify the standard behavior of the pattern.

The search() function scans the string from left to right and finds the first location where the pattern produces a match. It returns a Match object if the search was successful or None otherwise.

Python regex search() function examples

Let’s take some examples of using the search() function.

1) Using the Python regex search() fuction to find the first match

The following example uses the search() function to find the first number in the string:

import re

s = 'Python 3 was released on Dec 3, 2008'
pattern = '\d+'

match = re.search(pattern, s)

if match is not None:
    print(match.group())
else:
    print('No match found')Code language: Python (python)

Output:

<re.Match object; span=(7, 8), match='3'>Code language: Python (python)

In this example, the pattern \d+ matches one or more digits. The search() returns a Match object.

To get the match, you can call the group() method of the Match object like this:

import re

s = 'Python 3 was released on Dec 3, 2008'
pattern = '\d+'


match = re.search(pattern, s)

if match is not None:
    print(match.group())Code language: Python (python)

Output:

3Code language: Python (python)

2) Using the Python regex search() function to find the first word that matches a pattern

The following example uses the search() function to search the first word that ends with the literal string thon in a string:

import re

s = 'CPython, IronPython, or Cython'
pattern = r'\b((\w+)thon)\b'

match = re.search(pattern, s)

if match is not None:
    print(match.groups())Code language: Python (python)

Output:

('CPython', 'CPy')Code language: Python (python)

The pattern r'\b((\w+)thon)\b' has two capturing groups:

• (\w+) – captures the characters at the beginning of the word.
• ((\w+)thon) – captures the whole word.

The search() function returns the first location where it finds the match. To access all the groups in a match, you use the groups() method of the match object.

As clearly shown in the output, the groups() method returns a tuple that contains all the groups.

3) Using the Python regex search() function with a regex flag

The following example uses the search() function to find the first python word in a string:

import re

s = 'Python or python'
pattern = r'\bpython\b'

match = re.search(pattern, s)
print(match)Code language: Python (python)

It returns the word python with the letter p in lowercase as specified in the pattern.

<re.Match object; span=(10, 16), match='python'>Code language: Python (python)

To match the word case-insensitively, you can pass the re.IGNORECASE flag to the third argument of the search() function. For example:

import re

s = 'Python or python'
pattern = r'\bpython\b'

match = re.search(pattern, s, re.IGNORECASE)
print(match)Code language: Python (python)

In this example, the search() function returns the word Python with the letter P in uppercase:

<re.Match object; span=(0, 6), match='Python'>Code language: Python (python)

Summary

• Use the regex search() function to return the first match of a pattern in a string or None if the search was unsuccessful.