Case-Insensitive Python Regular Expression Without Re-Compile

By default, Python regular expressions (regex) look for case-sensitive matches. That is, the terms "apple" and "Apple" are not synonyms. But sometimes we want to search without consideration for uppercase or lowercase.

This is referred to as a case-insensitive match. This chapter teaches you how to create case-insensitive regexes in Python without using re.compile().

What is a Regular Expression?

A regular expression (regex) is a pattern that enables you to find strings like -

• Emails

• Phone Numbers

• Names

• Or any pattern.

To interact with regular expressions, we use the Python built-in module re.

Import the re Module

Before you use regex make sure you always import the re module -

import re

How to Make Regex Case-Insensitive Without re.compile

You can make your regex case-insensitive by providing the flags=re.IGNORECASE argument ?

re.function(pattern, string, flags=re.IGNORECASE)

Here you can replace the function with -

• search

• match

• findall

• sub, etc.

Using Case Insensitive Regular Expressions

In the following example, let us assume 'Python is a versatile programming language.' as a string. Here we have to find the occurrences of the word 'python' regardless of its case.

Example

The following Python code shows how to perform a case-insensitive search in a string using regular expressions. We can set the case-insensitive flag directly in the function call, which removes the need to create the regex pattern.

import re

text = "Python is a versatile programming language."
matches = re.findall(r"python", text, re.IGNORECASE)
print(matches)

In this example, we utilize the re.IGNORECASE flag within the call to re.findall() to ensure that the search is case insensitive.

On executing the above code snippet, the below output is obtained.

['Python']

Using re.search() for Case Insensitivity

Take this example: 'Learning Python can be fun.' We want to find the occurrence of the word 'learning' in a case-insensitive manner.

Example

Here, we will use the re.search() function instead, which searches for the pattern in the string. The case insensitivity flag will again be included directly in the function call.

import re

text = "Learning Python can be fun."
match = re.search(r"learning", text, re.IGNORECASE)
if match:
    print(f"Found: {match.group()}")
else:
    print("Not found")

The re.search() function returns a match object if the pattern is found; otherwise, it returns None.

On executing the above code snippet, the below output is obtained.

Found: Learning

Using re.sub() for Case Insensitive Replacements

In our next example, consider 'Python is great for data science.'. We will replace the word 'great' with 'fantastic' in a case-insensitive manner.

Example

We will make use of the re.sub() function, which allows us to replace patterns found in strings. The case insensitivity flag will be applied directly within the function call.

import re

text = "Python is great for data science."
new_text = re.sub(r"great", "fantastic", text, flags=re.IGNORECASE)
print(new_text)

The re.sub() function returns a new string with all occurrences of the pattern replaced by the specified replacement string.

On executing the above code snippet, the following output is obtained.

Python is fantastic for data science.