Python Regular Expressions (re module): Syntax, Functions, and Examples

Regular expressions (regex) are logical formulas for matching patterns in strings, using special characters called metacharacters. In Python, the re module provides full regex functionality.

The module offers functions such as re.match() , re.search() , and re.sub() , each taking a pattern, a target string, and optional flags.

re.match() attempts to match the pattern only at the beginning of the string and returns a match object or None . Example:

re.match(pattern, string, flags=0)

# Example
import re
line = 'i can speak good english'
matchObj = re.match(r'\s(\w*)\s(\w*).*', line)
if matchObj:
    print('matchObj.group() :', matchObj.group())
    print('matchObj.group() :', matchObj.group(1))
    print('matchObj.group() :', matchObj.group(2))
    print('matchObj.group() :', matchObj.group(3))
else:
    print('no match!')

re.search() scans the entire string and returns the first occurrence of the pattern. Example:

re.search(pattern, string, flags=0)

# Example
import re
line = 'i can speak good english'
matchObj = re.search('(.*) (.*?) (.*)', line)
if matchObj:
    print('matchObj.group() :', matchObj.group())
    print('matchObj.group() :', matchObj.group(1))
    print('matchObj.group() :', matchObj.group(2))
    print('matchObj.group() :', matchObj.group(3))
else:
    print('no match!')

re.sub() replaces occurrences of the pattern with a replacement string. Syntax:

re.sub(pattern, repl, string, max=0)

# Example
import re
line = 'i can speak good english'
speak = re.sub(r'can', 'not', line)
print(speak)
speak1 = re.sub(r'\s', '', line)  # remove all spaces
print(speak1)

The tutorial also covers special regex constructs such as character classes, predefined character sets, quantifiers, non‑greedy matching, grouping with parentheses, back‑references, anchors, and other advanced syntaxes, illustrated with diagrams.