Character classes

• ^: The beginning of a line
• $: The end of a line
• \A: The beginning of a string
• \Z: The end of a string
• \b: A word boundary
• \B: Anything except a word boundary
• .: Any character except a newline (unless re.DOTALL is used)
• \d and D: Any (non-)digit
• \s and \S: Any (non-)whitespace character
• \w and \W: Any (non-)alphanumeric character
• [ and ]: Specify a character class, either as a set of characters (e.g.., [abc] or as a range (e.g. [a-c])
• ^: As the first character in a character class, negates the set (e.g., [^abc] matches any character except a, b, or c).

Repetitions

• *: Match the preceding character or group zero or more times.
• +: Match the preceding character or group one or more times.
• ?: Match the preceding character or group zero or one time.
• {m,n}: Match the preceding character or group between m and n times.

Operators

• \: Escape a metacharacter (e.g., \+ matches the character +).
• |: The or operator

Groups

• (...): Define a group
• (?P<name>...): Define a named group
• (?:...): Define a non-capturing group
• (?=...): Positive lookahead assertion
• (?!...): Negative lookahead assertion

Regex Functions in Python

• match: Retursn a match object iff the RE matches at the beginning of the string
• search: Returns a match object if the RE matches anywhere in the string
• finditer: Returns an iterator over substrings that match the RE
• sub: Replaces all substrings that match the RE with another RE
• split: Splits a string at every match to the RE
• compile: Convert a regular expression into a pattern object that can be re-used