re Questions

[Chris Angelico]

On Mon, Jan 27, 2014 at 3:59 AM, Blake Adams <blakesadams at gmail.com> wrote:
> If I want to set up a match replicating the '\w' pattern I would assume that would be done with '[A-z0-9_]'.  However, when I run the following:
>
> re.findall('[A-z0-9_]','^;z %C\@0~_') it matches ['^', 'z', 'C', '\\', '0', '_'].  I would expect the match to be ['z', 'C', '0', '_'].
>
> Why does this happen?

Because \w is not the same as [A-z0-9_]. Quoting from the docs:

"""
\w For Unicode (str) patterns:Matches Unicode word characters; this
includes most characters that can be part of a word in any language,
as well as numbers and the underscore. If the ASCII flag is used, only
[a-zA-Z0-9_] is matched (but the flag affects the entire regular
expression, so in such cases using an explicit [a-zA-Z0-9_] may be a
better choice).For 8-bit (bytes) patterns:Matches characters
considered alphanumeric in the ASCII character set; this is equivalent
to [a-zA-Z0-9_].
"""

If you're working with a byte string, then you're close, but A-z is
quite different from A-Za-z. The set [A-z] is equivalent to
[ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz] (that's
a literal backslash in there, btw), so it'll also catch several
non-alphabetic characters. With a Unicode string, it's quite
distinctly different. Either way, \w means "word characters", though,
so just go ahead and use it whenever you want word characters :)

ChrisA