Re: lstrip problem - beginner question

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Date	Tue, 04 Jun 2013 21:53:53 -0700
From	Larry Hudson <orgnut@yahoo.com>
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On 06/04/2013 08:21 AM, mstagliamonte wrote:
> Hi everyone,
>
> I am a beginner in python and trying to find my way through... :)
>
> I am writing a script to get numbers from the headers of a text file.
>
> If the header is something like:
> h01 = ('>scaffold_1')
> I just use:
> h01.lstrip('>scaffold_')
> and this returns me '1'
>
> But, if the header is:
> h02: ('>contig-100_0')
> if I use:
> h02.lstrip('>contig-100_')
> this returns me with: ''
> ...basically nothing. What surprises me is that if I do in this other way:
> h02b = h02.lstrip('>contig-100')
> I get h02b = ('_1')
> and subsequently:
> h02b.lstrip('_')
> returns me with: '1' which is what I wanted!
>
> Why is this happening? What am I missing?
>
> Thanks for your help and attention
> Max
>

The lstrip() function is the wrong one to use here.  The command help(str.lstrip) gives:

lstrip(...)
     S.lstrip([chars]) -> str

     Return a copy of the string S with leading whitespace removed.
     If chars is given and not None, remove characters in chars instead.

IOW, it does NOT strip the given string, but all the characters in the given string.
So in your second example it (correctly) removes everything and gives you an empty string as the 
result.

One possible alternative is to use slicing:

h02 = '>contig-100_0'
h03 = '>contig-100_'
result = h02[len(h03):]

Or some similar variation, possibly adding a startswith() function for some simple error 
checking.  Of course, other approaches are possible as well,

      -=- Larry -=-

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Thread

lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 08:21 -0700
  Re: lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 08:24 -0700
  Re: lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 08:25 -0700
    Re: lstrip problem - beginner question Fábio Santos <fabiosantosart@gmail.com> - 2013-06-04 16:41 +0100
      Re: lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 08:49 -0700
        Re: lstrip problem - beginner question Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-06-04 17:01 +0100
        Re: lstrip problem - beginner question Dave Angel <davea@davea.name> - 2013-06-04 17:48 -0400
  Re: lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 08:28 -0700
  Re: lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 08:29 -0700
  Re: lstrip problem - beginner question MRAB <python@mrabarnett.plus.com> - 2013-06-04 16:48 +0100
    Re: lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 08:53 -0700
  Re: lstrip problem - beginner question Peter Otten <__peter__@web.de> - 2013-06-04 17:52 +0200
  Re: lstrip problem - beginner question John Gordon <gordon@panix.com> - 2013-06-04 15:55 +0000
    Re: lstrip problem - beginner question mstagliamonte <madmaxthc@yahoo.it> - 2013-06-04 09:06 -0700
  Re: lstrip problem - beginner question Larry Hudson <orgnut@yahoo.com> - 2013-06-04 21:53 -0700

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