regular expression reverse match?

[Emile van Sebille]

"Ron Adam" <radam2 at tampabay.rr.com> wrote in message
news:fqcupvkic63mrb5hv1hbn1g06fggkdl91g at 4ax.com...
>
> Is it possible to match a string to regular expression pattern instead
> of the other way around?

You can abuse the implmentation details to discover the original search
string.

>
> For example,  instead of finding a match  within a string,  I want to
> find out, (pass or fail), if a string is a partial match to an re.
>
> Given an  re of   'abcd and a bunch of other stuff'

I'll assume you mean comething like:

x = re.compile('abcd and a bunch of other stuff')


>
> This is what i'm looking for:
>
> string  /  result
>   'a'  /  pass
> 'ab' /  pass
> 'abc'  / pass
> 'abd'  /  fail
> 'aaaa'  /  fail
> 'abcd and a bunch of other stuff and then some'  /  fail
>
> Is there a way to form a regular expression that will do this?

for k,v in re._cache.items():
    if v == x:
        ss=k[0]
        break

Then it's a normal:

>>> re.match('a',ss)
<_sre.SRE_Match object at 0x009828E0>
>>> re.match('abd',ss)
>>>


Not sure that's what you're looking for, but reasonably sure it won't work
in all cases.

HTH,

Emile van Sebille
emile at fenx.com