What is a regex to match ONLY an empty string?

Question

There are lots of posts about regexs to match a potentially empty string, but I couldn\'t readily find any which provided a regex which only matched an emp

Answer 1

I believe Python is the only widely used language that doesn't support \z in this way (yet). There are Python bindings for Russ Cox / Google's super fast re2 C++ library that can be "dropped in" as a replacement for the bundled re.

There's an excellent discussion (with workarounds) for this at Perl Compatible Regular Expression (PCRE) in Python, here on SO.

python
Python 2.7.11 (default, Jan 16 2016, 01:14:05) 
[GCC 4.2.1 Compatible FreeBSD Clang 3.4.1 on freebsd10
Type "help", "copyright", "credits" or "license" for more information.
>>> import re2 as re
>>> 
>>> re.match(r'\A\z', "")

@tchrist's answer is worth the read.