I thought Python regular expressions were Perl-compatible in syntax, and somewhere I guess I got the impression they used the PCRE backend, though I might have entirely imagined that. At least I thought the distinction between re and regex was that regex used Emacs-style regular expressions, and re used Perl-style.
But I'm not saying I'm right or anything.
In 1.5.2, the RE module used PCRE. In 1.6 and later, that was replaced with a Unicode-aware engine, SRE, which was written from scratch, using on the 1.5.2 documentation and test suite as the specification. (guess who wrote it? ;-)
should have been "using only the"