re module

Monty's re module is backed by the Rust fancy-regex crate, not CPython's regex engine. Most patterns behave identically, but the underlying engine differs in syntax extensions and error reporting.

Module functions

Implemented: compile, search, match, fullmatch, findall, sub, split, finditer, escape.

Not implemented: subn, purge, template. The pre-compiled re._compile internal is not exposed.

Flags

Supported: NOFLAG, IGNORECASE / I, MULTILINE / M, DOTALL / S, ASCII / A.

Not implemented: VERBOSE / X, LOCALE / L, DEBUG, UNICODE / U (Unicode is always on). Passing an unknown flag bit is silently accepted.

re.Pattern objects

Attributes: pattern, flags. Methods: search, match, fullmatch, findall, sub, split, finditer.

Not implemented: subn, groups (count), groupindex (named-group mapping), scanner. The pos / endpos arguments accepted by Pattern.search(string, pos, endpos) etc. in CPython are not supported.

re.Match objects

Attributes: re, string. Methods: group, groups, groupdict, start, end, span.

Not implemented: lastindex, lastgroup, expand, pos, endpos, regs. Indexing (m[0], m["name"]) is not supported — use .group().

re.PatternError / re.error

Raised for invalid regex patterns. Unlike CPython, pattern, pos, lineno, and colno attributes are not populated — fancy-regex's error representation does not carry them.

Engine-level differences

• Unsupported regex features (some Unicode property escapes, some CPython-specific extensions) raise re.PatternError at compile time.
• Backreference syntax \10 and higher is not recognized; only \1–\9.
• Error messages for invalid patterns come from fancy-regex and do not match CPython's wording.