Key Functions in the re Module

import re
result = re.match(r'\d+', '123abc')
print(result.group())  # Output: 123

result = re.search(r'\d+', 'abc123def')
print(result.group())  # Output: 123

Regular Expression Syntax

• Literal characters: Matches the exact characters. a matches 'a'.
• Meta-characters: Special characters that have a special meaning.
  • . - Matches any character except a newline.
  • ^ - Matches the start of the string.
  • $ - Matches the end of the string.
  • [] - Matches any single character within the brackets.
  • | - Matches either the pattern before or the pattern after the |.
• Quantifiers: Specify the number of occurrences.
  • * - Matches 0 or more repetitions.
  • + - Matches 1 or more repetitions.
  • ? - Matches 0 or 1 repetition.
  • {m} - Matches exactly m repetitions.
  • {m,n} - Matches between m and n repetitions.
• Groups and Backreferences:
  • () - Groups patterns and captures the matched sub-pattern.
  • \1, \2, ... - References to the captured groups.

Examples of Regular Expressions

Matching an email address:

import re
pattern = r'[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}'
result = re.findall(pattern, 'Contact us at info@example.com')
print(result)  # Output: ['info@example.com']

Matching a phone number:

pattern = r'\+?(\d{1,3})?[-.\s]?\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}'
result = re.findall(pattern, 'Call me at (123) 456-7890 or +1-123-456-7890')
print(result)  # Output: ['1234567890', '11234567890']

Further Reading

For more detailed information, refer to the official Python documentation on the re module.