Python Regex Quantifiers

Summary: in this tutorial, you’ll learn how to use Python regex quantifiers to define how many times a character or a character set can be repeated.

Introduction to Python regex quantifiers

In regular expressions, quantifiers match the preceding characters or character sets a number of times. The following table shows all the quantifiers and their meanings:

Match zero or more times (*)

The quantifier (*) matches its preceding element zero or more times. For example, the following program uses the * quantifier to match any string that ends with Python:

import re

s = """CPython, IronPython, and JPython 
       are major Python's implementation"""

matches = re.finditer('\w*Python', s)

for match in matches:
    print(match)Code language: Python (python)

In this example:

• The \w matches any single word character.
• So the \w* matches zero or more word characters.
• Therefore, the \w*Python match any zero or more characters followed by the string Python.

As a result, the \w*Python pattern matches CPython, IronPython, JPython, and Python in the string:

<re.Match object; span=(0, 7), match='CPython'>
<re.Match object; span=(9, 19), match='IronPython'>
<re.Match object; span=(25, 32), match='JPython'>  
<re.Match object; span=(51, 57), match='Python'>  Code language: Python (python)

Match one or more times (+)

The + quantifier matches its preceding element one or more times. For example, the \d+ matches one or more digits.

The following example uses the + quantifier to match one or more digits in a string:

import re

s = "Python 3.10 was released in 2021"

matches = re.finditer('\d+', s)

for match in matches:
    print(match)Code language: Python (python)

Output:

<re.Match object; span=(7, 8), match='3'>
<re.Match object; span=(9, 11), match='10'>   
<re.Match object; span=(28, 32), match='2021'>Code language: Python (python)

Match zero or one time (?)

The ? quantifier matches its preceding element zero or one time.

The following example uses the (?) quantifier to match both strings color and colour:

import re

s = "What color / colour do you like?"

matches = re.finditer('colou?r', s)

for match in matches:
    print(match)Code language: Python (python)

Output:

<re.Match object; span=(5, 10), match='color'>
<re.Match object; span=(13, 19), match='colour'>Code language: Python (python)

In this example, the u? matches zero or one character u. Therefore, the colou?r pattern matches both color and colour

Match Exactly n Times: {n}

The {n} quantifier matches its preceding element exactly n times, where n is zero or a positive integer.

For example, the following program uses the quantifier {n} to match a time string in the hh:mm format:

import re

s = "It was 11:05 AM"

matches = re.finditer('\d{2}:\d{2}', s)

for match in matches:
    print(match)Code language: Python (python)

Output:

<re.Match object; span=(7, 12), match='11:05'>Code language: Python (python)

In this example, the \d{2} matches exactly two digits. Therefore, the \d{2}:\d{2} matches a string that starts with two digits, a colon :, and ends with two digits.

Match at least n times: {n,}

The {n,} quantifier matches its preceding element at least n times, where n is zero or a positive integer.

For example, the following program uses the {n, } quantifier to match the date strings with the m-d-yyyy or mm-dd-yyyy format:

import re

s = "5-5-2021 or 05-05-2021 or 5/5/2021"

matches = re.finditer('\d{1,}-\d{1,}-\d{4}', s)

for match in matches:
    print(match)Code language: Python (python)

Output:

<re.Match object; span=(0, 8), match='5-5-2021'>
<re.Match object; span=(12, 22), match='05-05-2021'>Code language: Python (python)

Match from n and m times: {n,m}

The {n,m} quantifier matches its preceding element at least n times, but no more than m times, where n and m are zero or a positive integer. For example:

import re

s = "5-5-2021 or 05-05-2021 or 5/5/2021"

matches = re.finditer('\d{1,2}-\d{1,2}-\d{4}', s)

for match in matches:
    print(match)Code language: Python (python)

Output:

<re.Match object; span=(0, 8), match='5-5-2021'>
<re.Match object; span=(12, 22), match='05-05-2021'>Code language: Python (python)

In this example, the pattern \d{1,2} matches one or two digits. So the pattern \d{1,2}-\d{1,2}-\d{4} matches a date string in the d-m-yyyy or dd-mm-yyyy format.

Summary

• Quantifiers match their preceding elements a number of times.