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Re: how to avoid leading white spaces

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On 2011-06-03, rurpy@yahoo.com <rurpy@yahoo.com> wrote:
>>> or that I have to treat commas as well as spaces as
>>> delimiters.
>>
>> source.replace(",", " ").split(" ")
>
> Uhgg. create a whole new string just so you can split it on one
> rather than two characters?  Sorry, but I find
>
>     re.split ('[ ,]', source)

It's quibbling to complain about creating one more string in an
operation that already creates N strings.

Here's another alternative:

list(itertools.chain.from_iterable(elem.split(" ") 
  for elem in source.split(",")))

It's weird looking, but delimiting text with two different
delimiters is weird.

> states much more clearly exactly what is being done with no
> obfuscation.  Obviously this is a simple enough case that the
> difference is minor but when the pattern gets only a little
> more complex, the clarity difference becomes greater.

re.split is a nice improvement over str.split. I use it often.
It's a happy place in the re module. Using a single capture group
it can perhaps also be used for applications of str.partition.

> I would not recommend you use a regex instead of a string
> method solely because you might need a regex later.  But when
> you have to spend 10 minutes writing a half-dozen lines of
> python versus 1 minute writing a regex, your evaluation of the
> possibility of requirements changing should factor into your
> decision.

Most of the simplest and clearest applications of the re module
are simply not necessary at all. If I'm inspecting a string with
what amounts to more than a couple of lines of basic Python then
break out the re module.

Of course often times that means I've got a context sensitive
parsing job on my hands, and I have to put it away again. ;)

> Yes, as I said, the regex attitude here seems in large part to
> be a reaction to their frequent use in Perl.  It seems anti- to
> me in that I often see cautions about their use but seldom see
> anyone pointing out that they are often a better solution than
> a mass of twisty little string methods and associated plumbing.

That doesn't seem to apply to the problem that prompted your
complaint, at least.

>> There are a few problems with regexes:
>>
>> - they are another language to learn, a very cryptic a terse
>> language;
>
> Chinese is cryptic too but there are a few billion people who
> don't seem to be bothered by that.

Chinese *would* be a problem if you proposed it as the solution
to a problem that could be solved by using a persons native
tongue instead.

>> - hence code using many regexes tends to be obfuscated and
>> brittle;
>
> No.  With regexes the code is likely to be less brittle than a
> dozen or more lines of mixed string functions, indexes, and
> conditionals.

That is the opposite of my experience, but YMMV.

>> - they're over-kill for many simple tasks;
>> - and underpowered for complex jobs, and even some simple ones;
>
> Right, like all tools (including Python itself) they are suited
> best for a specific range of problems.  That range is quite
> wide.
>
>> - debugging regexes is a nightmare;
>
> Very complex ones, perhaps.  "Nightmare" seems an
> overstatement.

I will abandon a re based solution long before the nightmare.

>> - they're relatively slow;
>
> So is Python.  In both cases, if it is a bottleneck then
> choosing another tool is appropriate.

It's not a problem at all until it is.

>> - and thanks in part to Perl's over-reliance on them, there's
>> a tendency among many coders (especially those coming from
>> Perl) to abuse and/or misuse regexes; people react to that
>> misuse by treating any use of regexes with suspicion.
>
> So you claim.  I have seen more postings in here where
> REs were not used when they would have simplified the code,
> then I have seen regexes used when a string method or two
> would have done the same thing.

Can you find an example or invent one? I simply don't remember
such problems coming up, but I admit it's possible.

-- 
Neil Cerutti

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Re: how to avoid leading white spaces Chris Rebert <clp2@rebertia.com> - 2011-06-01 10:11 -0700
  Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-01 12:39 -0700
    Re: how to avoid leading white spaces Karim <karim.liateni@free.fr> - 2011-06-01 22:34 +0200
    Re: how to avoid leading white spaces Neil Cerutti <neilc@norwich.edu> - 2011-06-02 13:21 +0000
      Re: how to avoid leading white spaces Roy Smith <roy@panix.com> - 2011-06-02 21:57 -0400
        Re: how to avoid leading white spaces MRAB <python@mrabarnett.plus.com> - 2011-06-03 03:41 +0100
        Re: how to avoid leading white spaces Chris Torek <nospam@torek.net> - 2011-06-03 02:58 +0000
          Re: how to avoid leading white spaces Roy Smith <roy@panix.com> - 2011-06-02 23:44 -0400
            Re: how to avoid leading white spaces Chris Angelico <rosuav@gmail.com> - 2011-06-03 13:52 +1000
            Re: how to avoid leading white spaces Chris Angelico <rosuav@gmail.com> - 2011-06-03 13:54 +1000
            Re: how to avoid leading white spaces Chris Torek <nospam@torek.net> - 2011-06-03 04:30 +0000
              Re: how to avoid leading white spaces Nobody <nobody@nowhere.com> - 2011-06-03 14:11 +0100
          Re: how to avoid leading white spaces Nobody <nobody@nowhere.com> - 2011-06-03 14:18 +0100
          Re: how to avoid leading white spaces Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-06-04 13:41 +1200
            Re: how to avoid leading white spaces Nobody <nobody@nowhere.com> - 2011-06-04 20:44 +0100
          Re: how to avoid leading white spaces Ian <hobson42@gmail.com> - 2011-06-06 22:04 +0100
            Re: how to avoid leading white spaces Chris Torek <nospam@torek.net> - 2011-06-09 02:32 +0000
        Re: how to avoid leading white spaces Thorsten Kampe <thorsten@thorstenkampe.de> - 2011-06-03 10:32 +0200
      Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-03 05:51 -0700
        Re: how to avoid leading white spaces Neil Cerutti <neilc@norwich.edu> - 2011-06-03 13:17 +0000
          Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-03 08:14 -0700
        Re: how to avoid leading white spaces Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-03 14:25 +0000
          Re: how to avoid leading white spaces "D'Arcy J.M. Cain" <darcy@druid.net> - 2011-06-03 10:58 -0400
          Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-03 12:29 -0700
            Re: how to avoid leading white spaces Neil Cerutti <neilc@norwich.edu> - 2011-06-03 20:49 +0000
              Re: how to avoid leading white spaces Chris Torek <nospam@torek.net> - 2011-06-03 21:45 +0000
                Re: how to avoid leading white spaces Ethan Furman <ethan@stoneleaf.us> - 2011-06-03 15:11 -0700
                Re: how to avoid leading white spaces MRAB <python@mrabarnett.plus.com> - 2011-06-03 23:38 +0100
                Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-05 22:47 -0700
              Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-05 22:44 -0700
                Re: how to avoid leading white spaces Neil Cerutti <neilc@norwich.edu> - 2011-06-06 16:08 +0000
                Re: how to avoid leading white spaces Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-06 10:29 -0600
                Re: how to avoid leading white spaces Neil Cerutti <neilc@norwich.edu> - 2011-06-06 17:17 +0000
                Re: how to avoid leading white spaces Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-06 11:40 -0600
                Re: how to avoid leading white spaces Neil Cerutti <neilc@norwich.edu> - 2011-06-06 17:56 +0000
                Re: how to avoid leading white spaces Ethan Furman <ethan@stoneleaf.us> - 2011-06-06 10:48 -0700
                Re: how to avoid leading white spaces Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-06 11:42 -0600
            Re: how to avoid leading white spaces Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-04 02:05 +0000
              Re: how to avoid leading white spaces MRAB <python@mrabarnett.plus.com> - 2011-06-04 03:24 +0100
                Re: how to avoid leading white spaces Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-04 04:59 +0000
              Re: how to avoid leading white spaces Roy Smith <roy@panix.com> - 2011-06-03 22:30 -0400
                Re: how to avoid leading white spaces Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-04 05:14 +0000
                Re: how to avoid leading white spaces Roy Smith <roy@panix.com> - 2011-06-04 09:39 -0400
                Re: how to avoid leading white spaces Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-05 00:44 +0000
                Re: how to avoid leading white spaces rusi <rustompmody@gmail.com> - 2011-06-04 09:36 -0700
                Re: how to avoid leading white spaces Nobody <nobody@nowhere.com> - 2011-06-04 21:02 +0100
                Re: how to avoid leading white spaces Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-05 01:01 +0000
                Re: how to avoid leading white spaces Chris Angelico <rosuav@gmail.com> - 2011-06-04 16:04 +1000
              Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-05 23:03 -0700
                Re: how to avoid leading white spaces Chris Torek <nospam@torek.net> - 2011-06-06 07:11 +0000
                Re: how to avoid leading white spaces "Octavian Rasnita" <orasnita@gmail.com> - 2011-06-06 11:51 +0300
                Re: how to avoid leading white spaces Chris Angelico <rosuav@gmail.com> - 2011-06-06 19:01 +1000
                Re: how to avoid leading white spaces rusi <rustompmody@gmail.com> - 2011-06-06 07:33 -0700
                Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-07 11:37 -0700
                Re: how to avoid leading white spaces Roy Smith <roy@panix.com> - 2011-06-07 20:30 -0400
                Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-08 07:38 -0700
                Re: how to avoid leading white spaces rusi <rustompmody@gmail.com> - 2011-06-08 09:14 -0700
                Re: how to avoid leading white spaces rusi <rustompmody@gmail.com> - 2011-06-08 01:27 -0700
                Re: how to avoid leading white spaces Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-06 15:29 +0000
                Re: how to avoid leading white spaces Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-06 10:06 -0600
                Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-07 09:00 -0700
                Re: how to avoid leading white spaces Duncan Booth <duncan.booth@invalid.invalid> - 2011-06-08 09:01 +0000
                Re: how to avoid leading white spaces "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-06-08 07:39 -0700
          Re: how to avoid leading white spaces rusi <rustompmody@gmail.com> - 2011-06-05 04:17 -0700

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