regex question

[proctor]

Paul McGuire wrote:
> "proctor" <12cc104 at gmail.com> wrote in message
> news:<1168232001.377605.236270 at 11g2000cwr.googlegroups.com>...
> > hello,
> >
> > i hope this is the correct place...
> >
> > i have an issue with some regex code i wonder if you have any insight:
> >
> > ================
>
> There's nothing actually *wrong* wth your regex.  The problem is your
> misunderstanding of raw string notation.  In building up your regex, do not
> start the string with "r'" and end it with a "'".
>
> def makeRE(w):
>     print w + " length = " + str(len(w))
>     # reString = "r'" + w[:1]
>     reString = w[:1]
>     w = w[1:]
>     if len(w) > 0:
>         for c in (w):
>             reString += "|" + c
>         # reString += "'"
>     print "reString = " + reString
>     return reString
>
> Or even better:
>
> def makeRE(w):
>     print w + " length = " + str(len(w))
>     reString = "|".join(list(w))
>     return reString
>
> Raw string notation is intended to be used when the string literal is in
> your Python code itself, for example, this is a typical use for raw strings:
>
> ipAddrRe = r'\d{1,3}(\.\d{1,3}){3}'
>
> If I didn't have raw string notation to use, I'd have to double up all the
> backslashes, as:
>
> ipAddrRe = '\\d{1,3}(\\.\\d{1,3}){3}'
>
> But no matter which way I create the string, it does not actually start with
> "r'" and end with "'", those are just notations for literals that are part
> of your Python source.
>
> Does this give you a better idea of what is happening?
>
> -- Paul

yes!  thanks so much.

it does work now...however, one more question:  when i type:

rx_a = re.compile(r'a|b|c')
it works correctly!

shouldn't:
rx_a = re.compile(makeRE(test))
give the same result since makeRE(test)) returns the string "r'a|b|c'"

are you saying that the "r'" and "'" are being interpreted differently
in the second case than in the first?  if so, how would i go about
using raw string notation in such a circumstance (perhaps if i need to
escape "\b" or the like)?  do i have to double up in this case?

proctor.