Every once in a while, I find the need to use regular expressions in Python programs. Most of the time, my needs are simple, such as: check if a string contains a word, where the word may have first letter capitalized.

Looking for a pattern at beginning of a string

In Python, regular expression functionality is provided by re module. And the most basic function to perform regular expression matching is the match() function.

match() accepts two arguments (and an optional third argument which we will not discuss in this post). The first argument is the pattern we are looking for and the second argument is the string we want to search in.

match() looks for the pattern at the beginning of the string.

Using in a conditional

import re

if re.match("[lL]orem", "Lorem ipsum dolor sit amet."):
    print("not matched")

The above conditional works because:

  • match() returns None if there is no match
  • returns a match object if there is a match
  • presense of an object (the match object) makes the return value have truthy value of True
  • since None is equivalent to boolean value False, we can use re.match() directly in a conditional as shown above.

While match() may satisfy many search requirements, it has one obvious limitation - match() looks for pattern only at the beginning of the string. The re module provides the function search() which overcomes this limitation. Function search() looks for the pattern anywhere in the string.

As we did with match() above, we can use search() in a simple conditional, as follows:

if re.search("[dD]olor", "Lorem ipsum dolor sit amet."):
    print("match found")
    print("match not found")

Here, we are looking for the pattern that occurs anywhere in the string, not just at the beginning. If the pattern is present, the if condition will evaluate to True. If there is no match then search() returns None which evaluates to truthy value of False.

Basic string match without using regular expressions

While this post is about using regular expressions, simple searches can be done using string operations:

in operator

if "dolor" in "Lorem ipsum dolor sit amet.":
    print("match found")


if "dolor" in "Lorem ipsum DOLOR sit amet.".lower():
    print("match found")

comparison operators

  • ”==” and “!=” operators can be used to compare equivalence of two strings.


In this post, I wanted to write about basic usage of regular expressions within python programs. Python’s re module provides a lot more functionality than described here.