String-SIG: Books

Compilers: Principles, Techniques, & Tools; Alfred V. Aho, Ravi Sethi, and Jeffrey D. Ullman; Hardcover.

Mastering Regular Expressions; Jeffrey E. F. Friedl; Paperback.

Covers regular expressions in great detail, including Python's regex module. Unfortunately the book was written before the re module was added to Python 1.5, so the book doesn't cover it, but it's still very useful as a guide to the new syntax, and to writing good regular expressions.

The Unicode Standard, Version 2.0; The Unicode Consortium; Paperback.