regular expression reverse match?

[Ron Adam]

On Tue, 28 Oct 2003 20:09:38 -0800, "Emile van Sebille"
<emile at fenx.com> wrote:

>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)
>>>>
>


Hi again Emile,

I tried it and get an error.
Here's my result.  Am I missing something?

>>> 
>>> import re
>>> x = re.compile('abcd and a bunch of other stuff')
>>> for k,v in re._cache.items():
	if v==x:
		ss=k[0]
		break

	
Traceback (most recent call last):
  File "<pyshell#21>", line 1, in ?
    for k,v in re._cache.items():
AttributeError: 'module' object has no attribute '_cache'
>>> 


With a trial and error method, (works for me eventually), this is what
I've been able to get to work so far.  I found the '$' is what I
needed to limit the buffer length to the pattern.

e = kb_input('Enter "Y" or "N" please: ', '[YyNn]$')
 f = kb_input('Enter "yes" please: ', 'y$|ye$|yes$')
g = kb_input('Enter "yes" or "no": ', '(y$|ye$|yes$)|(n$|no$)')
h = kb_input('Enter a 5 digit number:','\d$|\d{2}$\d{3}$\d{4}$\d{5}$')

New problem:    Is there a way to expand an re from:

'yes$'  to   'y$|ye$|yes$'

and

'(yes$)|(no$)' to  '(y$|ye$|yes$)|(n$|no$)'

and 

'\d{30}$'  to  '\d{1}$|\d{2}$|\d{3}$|\d{4}$|\d{5}$|  .......'


Other expressions that I might use would be:

'\d{3}-\d{3}-d\{4}$'    to match a phone number

or '\c{40}'   to specify a character string 40 characters long.

but if I have to manually expend these to the above formats they can
get pretty long.

''abcd and a bunch of other stuff'  becomes...
'a$|ab$|abc$|abcd$|abcd $|abcd a$|abc... etc...  etc...  ....stuff$'

Well at least I know what the re's look like now.  Time to sleep on it
and see what tomorrow brings.

_Ron