Why does re.sub in Python not work correctly on this test case?

Question

Try this code.

test = \' az z bz z z stuff z  z \'
re.sub(r\'(\\W)(z)(\\W)\', r\'\\1_\\2\\3\', test)

This should replace all stand-alone z\'s w

Answer 1

You want to avoid capturing the whitespace. Try using the 0-width word break \b, like this:

re.sub(r'\bz\b', '_z', test)