How to use the "?" character in regular expressions to make a pattern optional?

Here’s how to use the “?” character in regular expressions to make a pattern optional:

In regular expressions, the “?” character is used as a quantifier to make the preceding token optional. This means that the pattern that precedes the “?” character can match either zero or one occurrences of the token. For example:

import re

pattern = r'colou?r'  # regex pattern to match "color" or "colour"
text1 = 'The sky is blue'
text2 = 'The favourite colour is red'

match1 = re.search(pattern, text1)
match2 = re.search(pattern, text2)

if match1:
  print(match1.group())  # Output: None (no match found)
if match2:
  print(match2.group())  # Output: 'colour'

This will match both “color” and “colour” in a flexible way, making the letter “u” optional. In this example, the re.search() function returns the first non-overlapping occurrence of the regex pattern in the given string. If the pattern is not found in the string, re.search() will return None.

You can modify the pattern to make different parts of the pattern optional or to match different types of substrings in the string.