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Re: Regular expressions

Path csiph.com!news.swapon.de!fu-berlin.de!uni-berlin.de!not-for-mail
From Tim Chase <python.list@tim.thechases.com>
Newsgroups comp.lang.python
Subject Re: Regular expressions
Date Thu, 5 Nov 2015 08:00:00 -0600
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On 2015-11-05 23:05, Steven D'Aprano wrote:
> Oh the shame, I knew that. Somehow I tangled myself in a knot,
> thinking that it had to be 1 *followed by* zero or more characters.
> But of course it's not a glob, it's a regex.

But that's a good reminder of fnmatch/glob modules too.  Sometimes
all you need is to express a simple glob, in which case using a
regexp can cloud the clarity.

The overarching principle is to go for clarity & simplicity, rather
than favoring built-ins/glob/regex/parser modules all the time.

Want to test for presence in a string?  Just use the builtin "a in b"
test.  At the beginning/end?  Use .startswith()/.endswith() for
clarity.  Need to check if a string is purely
digits/alpha/alphanumerics/etc?  Use the
string .is{alnum,alpha,decimal,digit,identifier,lower,numeric,printable,space,title,upper}
methods on the string.

For simple wild-carding, use the fnmatch module to do simple
globbing.

For more complex pattern matching, you've got regexps.

Finally, for occasions when you're searching for repeated/nested
structures, using an add-on module like pyparsing will give you
clearer code.

Oh, and with regexps, people should be less afraid of verbose
multi-line strings with commenting

  r = re.compile(r"""
    ^                       # start of the string
    (?P<year>\d{4})         # capture 4 digits
    -                       # a literal dash
    (?P<month>\d{1,2})      # capture 1-2 digits
    -                       # another literal dash
    (?P<day>\d{1,2})        # capture 1-2 digits
    _                       # a literal underscore
    (?P<accountnum>         # capture the account-number
      [A-Z]{1,3}               # 1-3 letters
      \d+                      # followed by 1+ digits
      )
    \.txt                   # the extension of the file (ignored)
    $                       # the end of the string
    """, re.VERBOSE)

They are a LOT easier to come back to if you haven't touched the code
for a year.

-tkc

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Thread

Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-02 20:09 -0500
  Re: Regular expressions MRAB <python@mrabarnett.plus.com> - 2015-11-03 01:19 +0000
    Re: Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-02 22:17 -0500
  Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-02 20:42 -0600
    Re: Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-02 22:17 -0500
      Re: Regular expressions Joel Goldstick <joel.goldstick@gmail.com> - 2015-11-02 22:58 -0500
        Re: Regular expressions rurpy@yahoo.com - 2015-11-02 20:23 -0800
          Re: Regular expressions Michael Torrie <torriem@gmail.com> - 2015-11-02 21:38 -0700
            Re: Regular expressions rurpy@yahoo.com - 2015-11-03 16:33 -0800
              Re: Regular expressions Michael Torrie <torriem@gmail.com> - 2015-11-03 19:04 -0700
                Re: Regular expressions Dan Sommers <dan@tombstonezero.net> - 2015-11-04 02:55 +0000
                Re: Regular expressions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-04 14:23 +1100
                Re: Regular expressions Michael Torrie <torriem@gmail.com> - 2015-11-03 20:47 -0700
                Re: Regular expressions Grant Edwards <invalid@invalid.invalid> - 2015-11-04 13:27 +0000
                Re: Regular expressions Nobody <nobody@nowhere.invalid> - 2015-11-04 05:05 +0000
                Re: Regular expressions Peter Otten <__peter__@web.de> - 2015-11-04 09:57 +0100
                Re: Regular expressions Steven D'Aprano <steve@pearwood.info> - 2015-11-05 13:28 +1100
                Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-04 20:48 -0600
                Re: Regular expressions Ben Finney <ben+python@benfinney.id.au> - 2015-11-05 14:03 +1100
                Re: Regular expressions Peter Otten <__peter__@web.de> - 2015-11-05 09:33 +0100
                Re: Regular expressions Steven D'Aprano <steve@pearwood.info> - 2015-11-05 23:05 +1100
                Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-05 08:00 -0600
                Re: Regular expressions Albert van der Horst <albert@spenarnc.xs4all.nl> - 2015-11-05 13:39 +0000
                Re: Regular expressions Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-11-04 08:00 -0500
                Re: Regular expressions Michael Torrie <torriem@gmail.com> - 2015-11-04 08:13 -0700
                Re: Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-04 18:00 -0500
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 16:24 -0800
                Re: Regular expressions Steven D'Aprano <steve@pearwood.info> - 2015-11-05 13:24 +1100
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 21:59 -0800
                Re: Regular expressions Christian Gollwitzer <auriocus@gmx.de> - 2015-11-05 09:18 +0100
                Re: Regular expressions rurpy@yahoo.com - 2015-11-06 11:52 -0800
                Re: Regular expressions Christian Gollwitzer <auriocus@gmx.de> - 2015-11-06 21:36 +0100
                Re: Regular expressions Larry Martell <larry.martell@gmail.com> - 2015-11-06 15:42 -0500
                Re: Regular expressions Chris Angelico <rosuav@gmail.com> - 2015-11-05 11:34 +1100
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 22:27 -0800
                Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-04 09:42 -0600
                Re: Regular expressions Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-11-05 20:55 +1300
                Re: Regular expressions Chris Angelico <rosuav@gmail.com> - 2015-11-05 19:06 +1100
                What does “grep” stand for? (was: Regular expressions) Ben Finney <ben+python@benfinney.id.au> - 2015-11-05 05:24 +1100
                Re: What does “grep” stand for? Christian Gollwitzer <auriocus@gmx.de> - 2015-11-04 20:38 +0100
                Re: What does “grep” stand for? Chris Angelico <rosuav@gmail.com> - 2015-11-05 11:42 +1100
                Re: What does “grep” stand for? Christian Gollwitzer <auriocus@gmx.de> - 2015-11-05 08:32 +0100
                Re: What does “grep” stand for? Chris Angelico <rosuav@gmail.com> - 2015-11-05 19:00 +1100
                Re: What does “grep” stand for? Random832 <random832@fastmail.com> - 2015-11-05 10:19 -0500
                Re: What does “grep” stand for? Grant Edwards <invalid@invalid.invalid> - 2015-11-05 18:29 +0000
                Re: What does “grep” stand for? Random832 <random832@fastmail.com> - 2015-11-05 14:56 -0500
                Re: What does “grep” stand for? Grant Edwards <invalid@invalid.invalid> - 2015-11-05 20:19 +0000
                Re: What does “grep” stand for? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-11-05 20:18 -0500
                Re: What does “grep” stand for? Larry Hudson <orgnut@yahoo.com> - 2015-11-05 19:36 -0800
                Re: What does “grep” stand for? Dan Sommers <dan@tombstonezero.net> - 2015-11-06 05:31 +0000
                Re: What does “grep” stand for? William Ray Wing <wrw@mac.com> - 2015-11-06 08:25 -0500
                Re: What does “grep” stand for? Larry Hudson <orgnut@yahoo.com> - 2015-11-06 19:21 -0800
                Re: What does ???grep??? stand for? Grant Edwards <invalid@invalid.invalid> - 2015-11-06 14:15 +0000
                Re: What does ???grep??? stand for? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-11-06 20:03 -0500
                Re: What does “grep” stand for? (was: Regular expressions) Tim Chase <python.list@tim.thechases.com> - 2015-11-04 13:05 -0600
                Re: Regular expressions Terry Reedy <tjreedy@udel.edu> - 2015-11-04 18:08 -0500
                Re: Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-04 18:29 -0500
              Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-03 21:12 -0600
              Re: Regular expressions Chris Angelico <rosuav@gmail.com> - 2015-11-04 14:26 +1100
              Re: Regular expressions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-04 14:48 +1100
                Re: Regular expressions Christian Gollwitzer <auriocus@gmx.de> - 2015-11-04 08:21 +0100
                Re: Regular expressions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-04 19:47 +1100
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 06:43 -0800
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 06:38 -0800
                Re: Regular expressions Chris Angelico <rosuav@gmail.com> - 2015-11-05 01:52 +1100
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 16:13 -0800
                Re: Regular expressions Chris Angelico <rosuav@gmail.com> - 2015-11-05 11:33 +1100
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 21:42 -0800
                Re: Regular expressions Steven D'Aprano <steve@pearwood.info> - 2015-11-05 13:26 +1100
                Re: Regular expressions Ben Finney <ben+python@benfinney.id.au> - 2015-11-05 14:07 +1100
                Re: Regular expressions rurpy@yahoo.com - 2015-11-04 21:54 -0800
                Re: Regular expressions Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-05 10:14 +0100
                Re: Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-04 18:02 -0500
                Re: Regular expressions Steven D'Aprano <steve@pearwood.info> - 2015-11-05 11:54 +1100
                Re: Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-05 10:07 -0500
                Re: Regular expressions rurpy@yahoo.com - 2015-11-06 12:46 -0800
          Re: Regular expressions Steven D'Aprano <steve@pearwood.info> - 2015-11-03 18:15 +1100
            Re: Regular expressions Nick Sarbicki <nick.a.sarbicki@gmail.com> - 2015-11-03 08:43 +0000
            Re: Regular expressions rurpy@yahoo.com - 2015-11-03 16:22 -0800
      Re: Regular expressions Denis McMahon <denismfmcmahon@gmail.com> - 2015-11-03 12:38 +0000
      Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-03 05:53 -0600
      Re: Regular expressions Joel Goldstick <joel.goldstick@gmail.com> - 2015-11-03 10:34 -0500
        Re: Regular expressions Seymore4Head <Seymore4Head@Hotmail.invalid> - 2015-11-03 11:10 -0500
          Re: Regular expressions Chris Angelico <rosuav@gmail.com> - 2015-11-04 03:20 +1100
            Re: Regular expressions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-04 14:35 +1100
              Re: Regular expressions Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-04 12:41 +0100
    Re: Regular expressions Grant Edwards <invalid@invalid.invalid> - 2015-11-03 14:56 +0000
  Re: Regular expressions Michael Torrie <torriem@gmail.com> - 2015-11-02 20:51 -0700
    Re: Regular expressions rurpy@yahoo.com - 2015-11-02 20:23 -0800
      Re: Regular expressions Michael Torrie <torriem@gmail.com> - 2015-11-02 21:33 -0700
      Re: Regular expressions Robin Koch <robin.koch@t-online.de> - 2015-11-03 23:58 +0100
  Re: Regular expressions Peter Otten <__peter__@web.de> - 2015-11-03 10:25 +0100
  Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-03 05:50 -0600
  Re: Regular expressions Peter Otten <__peter__@web.de> - 2015-11-03 15:00 +0100
    Re: Regular expressions Jussi Piitulainen <harvesting@makes.email.invalid> - 2015-11-03 17:12 +0200
      Irregular last line in a text file, was Re: Regular expressions Peter Otten <__peter__@web.de> - 2015-11-03 16:35 +0100
        Re: Irregular last line in a text file, was Re: Regular expressions Jussi Piitulainen <harvesting@makes.email.invalid> - 2015-11-03 18:42 +0200
      Re: Irregular last line in a text file, was Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-03 10:56 -0600
        Re: Irregular last line in a text file, was Re: Regular expressions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-04 14:39 +1100
          Re: Irregular last line in a text file, was Re: Regular expressions Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-11-04 10:07 +0000
          Re: Irregular last line in a text file, was Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-04 09:33 -0600
      Re: Irregular last line in a text file, was Re: Regular expressions Peter Otten <__peter__@web.de> - 2015-11-03 18:44 +0100
      Re: Irregular last line in a text file, was Re: Regular expressions Ian Kelly <ian.g.kelly@gmail.com> - 2015-11-03 11:33 -0700
      Re: Irregular last line in a text file, was Re: Regular expressions Ian Kelly <ian.g.kelly@gmail.com> - 2015-11-03 11:39 -0700
      Re: Irregular last line in a text file, was Re: Regular expressions Tim Chase <python.list@tim.thechases.com> - 2015-11-03 13:45 -0600
        Re: Irregular last line in a text file, was Re: Regular expressions Grant Edwards <invalid@invalid.invalid> - 2015-11-03 22:15 +0000

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