Regex Metacharacters
Regex Special Sequences
This note covers Python’s regular expression special Sequences. These Sequences provide shortcuts for commonly used patterns.
Important Note: Remember to import the re module before using any of these. import re
import re
Here’s a breakdown of common special Sequences:
\d: Matches any decimal digit (0-9). Equivalent to[0-9]].\D: Matches any non-digit character. Equivalent to[^0-9]].\w: Matches any alphanumeric character (a-z, A-Z, 0-9, and underscore _). Equivalent to[a-zA-Z0-9_]].\W: Matches any non-alphanumeric character. Equivalent to[^a-zA-Z0-9_]].\s: Matches any whitespace character (space, tab, newline).\S: Matches any non-whitespace character.\b: Matches a word boundary (the position between a word character and a non-word character). Useful for finding whole words.\B: Matches a non-word boundary..: Matches any character (except newline).
Examples:
text = "My phone number is 123-456-7890."
# Find all digits
digits = re.findall(r"\d", text)
print(f"Digits: {digits}")
# Find all words
words = re.findall(r"\b\w+\b", text) # \b ensures whole words are matched
print(f"Words: {words}")
# Find phone number (more complex example - requires more than just special sequences)
phone_number = re.search(r"\d{3}-\d{3}-\d{4}", text)
if phone_number:
print(f"Phone number: {phone_number.group(0)}")
Character Sets These provide an alternative way of defining patterns, often in conjunction with special Sequences.
Quantifiers These are used to specify how many times a character or group should appear. (e.g., +, *, ?, {n}, {n,}, {n,m})
Anchors These match positions within a string, not characters. (e.g., ^, $, \b, \B)
Groups and Capturing This covers capturing groups using parentheses () and accessing captured substrings.
Regex Metacharacters A comprehensive overview of metacharacters used in regex beyond special sequences.
Regex Methods in Python’s re module A complete reference to all methods within Python’s re module for working with Regular Expressions.