Python Regular Expressions (RegEx)

A regular expression, or RegEx, is a sequence of characters that defines a search pattern. Python’s re module provides functions for working with regular expressions.

1. Matching Patterns

The re.match() function searches for a pattern at the beginning of a string.

import re

pattern = r"hello"
text = "hello world"

match = re.match(pattern, text)
if match:
    print("Pattern found!")
else:
    print("Pattern not found!")

2. Searching Patterns

The re.search() function searches for a pattern anywhere in a string.

pattern = r"world"
text = "hello world"

match = re.search(pattern, text)
if match:
    print("Pattern found!")
else:
    print("Pattern not found!")

3. Finding All Matches

The re.findall() function finds all occurrences of a pattern in a string and returns them as a list.

pattern = r"lo"
text = "hello world"

matches = re.findall(pattern, text)
print(matches)  # Output: ['lo', 'lo']

4. Substituting Patterns

The re.sub() function substitutes occurrences of a pattern in a string with another string.

pattern = r"world"
text = "hello world"

new_text = re.sub(pattern, "Python", text)
print(new_text)  # Output: hello Python

Conclusion

Regular expressions are a powerful tool for pattern matching and text manipulation in Python. The re module provides functions for searching, matching, finding all occurrences, and substituting patterns in strings.