Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Terry Reedy <tjreedy@udel.edu>
Newsgroups: comp.lang.python
Subject: Re: Regex: Perl to Python
Date: Sun, 6 Mar 2016 23:48:47 -0500
Lines: 53
Message-ID: <mailman.7.1457326155.10335.python-list@python.org>
References: <nbj0k0$12gk$1@gioia.aioe.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: news.uni-berlin.de HZOYwGPCz2L5CiOiVxbXgQC1Obdl0ymNHzofkRJBTmyg==
Return-Path: <python-python-list@m.gmane.org>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.001
X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'subject:Python': 0.05; 'block.': 0.09; 'exiting': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'python': 0.10; 'python.': 0.11; 'jan': 0.11; 'skip:# 20': 0.13; 'motivator': 0.16; 'received:80.91.229.3': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'reedy': 0.16; 'statement.': 0.16; 'wrote:': 0.16; 'attribute': 0.18; 'string,': 0.18; '>>>': 0.20; 'trying': 0.22; 'seems': 0.23; 'import': 0.24; '(most': 0.24; 'header:In-Reply-To:1': 0.24; 'module': 0.25; 'header:User-Agent:1': 0.26; 'header:X-Complaints- To:1': 0.26; 'found.': 0.27; 'object,': 0.27; 'function': 0.28; 'perl': 0.29; "i'm": 0.30; 'print': 0.30; 'statement': 0.32; 'getting': 0.33; 'traceback': 0.33; 'file': 0.34; 'add': 0.34; 'returning': 0.35; 'something': 0.35; 'but': 0.36; 'to:addr :python-list': 0.36; 'pm,': 0.36; 'subject:: ': 0.37; 'received:org': 0.37; 'delete': 0.38; 'wrong': 0.38; 'files': 0.38; 'hi,': 0.38; 'why': 0.39; 'to:addr:python.org': 0.40; 'challenge': 0.61; '30,': 0.63; 'received:96': 0.63; "'if": 0.84; 'hardest': 0.91; 'received:fios.verizon.net': 0.91
X-Injected-Via-Gmane: http://gmane.org/
X-Gmane-NNTP-Posting-Host: pool-96-227-207-81.phlapa.fios.verizon.net
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0
In-Reply-To: <nbj0k0$12gk$1@gioia.aioe.org>
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.21
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <http://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Xref: csiph.com comp.lang.python:104185

On 3/6/2016 11:38 PM, Fillmore wrote:
>
> Hi, I'm trying to move away from Perl and go to Python.
> Regex seems to bethe hardest challenge so far.
>
> Perl:
>
> while (<HEADERFILE>) {
>      if (/(\d+)\t(.+)$/) {
>      print $1." - ". $2."\n";
>      }
> }
>
> into python
>
> pattern = re.compile(r"(\d+)\t(.+)$")
> with open(fields_Indexfile,mode="rt",encoding='utf-8') as headerfile:
>      for line in headerfile:
>          #sys.stdout.write(line)
>          m = pattern.match(line)
>          print(m.group(0))
>      headerfile.close()

Delete this line.  Files opened in a with statement are automatically 
closed when exiting the block.  This is a main motivator and use for the 
with statement.

> but I must be getting something fundamentally wrong because:
>
> Traceback (most recent call last):
>    File "./slicer.py", line 30, in <module>
>      print(m.group(0))
> AttributeError: 'NoneType' object has no attribute 'group'
>
>
>   why is 'm' a None?

Python has a wonderful interactive help facility.  Learn to use it.

 >>> import re
 >>> help(re.match)
Help on function match in module re:

match(pattern, string, flags=0)
     Try to apply the pattern at the start of the string, returning
     a match object, or None if no match was found.
 >>>

Add 'if m is not None:' before accessing m.group.

-- 
Terry Jan Reedy