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Date: Tue, 16 Jul 2013 13:38:35 +0200
From: "Anders J. Munch" <2013@jmunch.dk>
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To: ben@benlast.com
Subject: Re: grimace: a fluent regular expression generator in Python
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Xref: csiph.com comp.lang.python:50743

Ben Last wrote:
> north_american_number_re = (RE().start
>
> .literal('(').followed_by.exactly(3).digits.then.literal(')')
>                                      .then.one.literal("-").then.exactly(3).digits
>
> .then.one.dash.followed_by.exactly(4).digits.then.end
>                                      .as_string())

Very cool.  It's a bit verbose for my taste, and I'm not sure how well it will 
cope with nested structure.

Here's my take on what readable regexps could look like:

north_american_number_re = RE.compile(r"""
     ^
     "(" digit{3} ")"  # And why shouldn't a regexp
     "-" digit{3}      # include en embedded comment?
     "-" digit{4}
     $
""")

The problem with Perl-style regexp notation isn't so much that it's terse - it's 
that the syntax is irregular (sic) and doesn't follow modern principles for 
lexical structure in computer languages.  You can get a long way just by 
ignoring whitespace, putting literals in quotes and allowing embedded comments.

Setting the re.VERBOSE flag achieves two out of three, so you can write:

north_american_number_re = RE.compile(r"""
     ^
     ( \d{3} )   # Definite improvement, though I really miss putting
     - \d{3}     # literals in quotes.
     - \d{4}
     $
""")

It's too bad re.VERBOSE isn't the default.

regards, Anders