[Python-ideas] PEP 8: raw strings & regular expressions

[David Mertz]

Obviously there can't be a regex to exclude everything that isn't a regex.
Parentheses can nest to unlimited depths, so you need a formal grammar. But
virtually everything that is a Windows path is also formally grammatical
regex too (as are many things with no plausible likely intention as such)
On Oct 26, 2015 2:44 PM, "Ben Finney" <ben+python at benfinney.id.au> wrote:

> Andrew Barnert via Python-ideas
> <python-ideas at python.org> writes:
>
> > Just for fun: is there a Python regex that matches all valid Python
> > regexes?
>
> Yes: ‘.*’ matches all valid Python regexes.
>
> > Obviously there's no actual regular expression that matches all
> > regular expressions (you can't handle matched brackets without
> > recursion or some other extension).
>
> You seem to be seeking something else: a pattern that matches all valid
> regex patterns, *and* will never match any string that is not a valid
> regex pattern. The latter is rather more difficult.
>
> --
>  \      “When I was born I was so surprised I couldn't talk for a year |
>   `\                                        and a half.” —Gracie Allen |
> _o__)                                                                  |
> Ben Finney
>
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