Python Regex fullmatch()

Summary: in this tutorial, you’ll learn how to use the Python regex fullmatch() to match the whole string with a regular expression.

Introduction to the Python regex fullmatch function

The fullmatch() function returns a Match object if the whole string matches the search pattern of a regular expression, or None otherwise.

The syntax of the fullmatch() function is as follows:

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

In this syntax:

• pattern specifies a regular expression to match.
• string specifies the input string.
• flags parameter is optional and defaults to zero. The flags parameter accepts one or more regex flags. The flags parameter changes how the regex engine matches the pattern.

Python regex fullmatch function example

The following example uses the fullmatch() function to validate an email address:

import re

email = '[email protected]'
pattern = r'[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}'
match = re.fullmatch(pattern, email)

if match is not None:
    print(f'The email "{match.group()}" is valid')    
else:
    print(f'The email "{email}"" is not valid')Code language: Python (python)

Output:

The email "[email protected]" is validCode language: Python (python)

The following defines a function that uses the fullmatch() function to validate an email address. It returns True if the email is valid or raises a ValueError exception otherwise:

import re

def is_email(s: str) -> bool:
    pattern = r'[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}'
    if re.fullmatch(pattern, s) is None:
        raise ValueError(f'The {s} is not a valid email address')

    return TrueCode language: Python (python)

And you can use the is_email() function to validate an email like this:

if __name__ == '__main__':
    try:
       if is_email('no-reply@pythontutorial'):
           print('The email is valid')
    except ValueError as e:
        print(e)Code language: Python (python)

Output:

The no-reply@pythontutorial is not a valid email addressCode language: Python (python)

Python regex fullmatch vs match

Both fullmatch() and match() functions return a Match object if they find a match.

The fullmatch() function matches the whole string with a pattern while the match() function only finds a match at the beginning of the string. See the following example:

import re

s = 'Python 3'
pattern = 'Python'

# fullmatch
match = re.fullmatch(pattern, s)
if match is not None:
    print('fullmatch:', match.group())

# search
match = re.match(pattern, s)
if match is not None:
    print('match:', match.group())Code language: Python (python)

Output:

match: PythonCode language: Python (python)

In this example, the fullmatch() returns None because the pattern Python only matches the beginning of the string, not the whole string.

On the other hand, the match() function matches the pattern at the beginning of the string and returns the match.

Python fullmatch vs. search

Both fullmatch() and search() functions return a Match object if they find a match of a pattern in a string. However, the fullmatch() matches the whole string while the search() matches anywhere in the string.

For example:

import re

s = 'Python 3'
pattern = '\d'

# fullmatch
match = re.fullmatch(pattern,s)
if match is not None:
    print(match.group()) 

# search
match = re.search(pattern,s)
if match is not None:
    print(match.group()) # 3Code language: Python (python)

Output:

3Code language: Python (python)

In this example, the pattern \d matches a single digit. The fullmatch() function returns None because the whole string 'Python 3' doesn’t match.

However, the search() function returns a match because it could find the digit 3 at the end of the string.

Summary

• Use the Python regex fullmatch() function to check if the whole string matches a pattern of a regular expression.