re.compile versus r''

[Chris Rebert]

On Thu, Aug 28, 2008 at 12:23 PM, Terrence Brannon <metaperl at gmail.com> wrote:
> Hello, I'm using a tool (PLY) which apparently expects the tokens to
> be created using r''
>
> But because one token is a rather complex regular expression, I want
> to create the regular expression programmatically.
>
> How can I generate a string and then create something of the same type
> that the r'' function does?

The "r" prefix isn't a function or a type, it's merely a special
literal syntax for strings that's handy when you're writing regexes
and therefore have to deal with another level of backslash escaping.
See the second to last paragraph of
http://docs.python.org/ref/strings.html  for more info.

Regards,
Chris

>
> Concretely, in the program below, consonant is not the same type as
> t_NAME, but I assume that it needs to be for PLY to use it for
> tokenizing:
>
> import re
>
> t_NAME       = r'[a-zA-Z_][a-zA-Z0-9_]*'
>
> guttural   = 'kh?|gh?|\"n'
> palatal    = '(?:chh?|jh?|\~n)'
> cerebral   = '\.(?:th?|dh?|n)'
> dental     = '(?:th?|dh?|n)'
> semivowel  = '[yrlv]'
> sibilant   = '[\"\.]?s'
> aspirant   = 'h'
>
> consonant = re.compile('|'.join([guttural , palatal , cerebral ,
> dental , semivowel , sibilant , aspirant]))
>
> print consonant
> print t_NAME
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>