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Re: Running a command line program and reading the result as it runs

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Subject Re: Running a command line program and reading the result as it runs
Date Fri, 23 Aug 2013 12:04:14 -0400
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On Fri, Aug 23, 2013, at 7:14, Peter Otten wrote:
> The following works on my linux system:
> 
> instream = iter(p.stdout.readline, "")
>         
> for line in instream:
>     print line.rstrip()
> 
> I don't have Windows available to test, but if it works there, too, the 
> problem is the internal buffer used by Python's implementation of file 
> iteration rather than the OS.

I can confirm this on Windows.

Doesn't this surprising difference between for line in
iter(f.readline,'') vs for line in f violate TOOWTDI? We're led to
believe from the documentation that iterating over a file does _not_
read lines into memory before returning them. It's not clear to me what
performance benefit can be gained from waiting when there is no more
data available, either.

I don't understand how it's even happening - from looking at the code,
it looks like next() just calls readline() once, no fancy buffering
specific to itself.

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Thread

Running a command line program and reading the result as it runs Ian Simcock <Ian.Simcock@Internode.on.net> - 2013-08-22 15:21 +0930
  Re: Running a command line program and reading the result as it runs Chris Angelico <rosuav@gmail.com> - 2013-08-22 16:22 +1000
    Re: Running a command line program and reading the result as it runs Ian Simcock <Ian.Simcock@Internode.on.net> - 2013-08-23 00:56 +0930
      Re: Running a command line program and reading the result as it runs Chris Angelico <rosuav@gmail.com> - 2013-08-23 01:33 +1000
        Re: Running a command line program and reading the result as it runs Ian Simcock <Ian.Simcock@Internode.on.net> - 2013-08-23 16:22 +0930
        Re: Running a command line program and reading the result as it runs Grant Edwards <invalid@invalid.invalid> - 2013-08-23 14:02 +0000
  Re: Running a command line program and reading the result as it runs Rob Wolfe <rw@smsnet.pl> - 2013-08-22 23:14 +0200
    Re: Running a command line program and reading the result as it runs Ian Simcock <Ian.Simcock@Internode.on.net> - 2013-08-23 16:31 +0930
  Re: Running a command line program and reading the result as it runs Gertjan Klein <gklein@xs4all.nl> - 2013-08-23 11:32 +0200
  Re: Running a command line program and reading the result as it runs Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-23 11:53 +0200
  Re: Running a command line program and reading the result as it runs Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-08-23 12:34 +0200
  RE: Running a command line program and reading the result as it runs "Joseph L. Casale" <jcasale@activenetwerx.com> - 2013-08-23 10:50 +0000
  Re: Running a command line program and reading the result as it runs Peter Otten <__peter__@web.de> - 2013-08-23 13:14 +0200
    Re: Running a command line program and reading the result as it runs Gertjan Klein <gklein@xs4all.nl> - 2013-08-23 14:03 +0200
    Re: Running a command line program and reading the result as it runs Ian Simcock <Ian.Simcock@Internode.on.net> - 2013-08-24 19:06 +0930
  Re: Running a command line program and reading the result as it runs random832@fastmail.us - 2013-08-23 12:04 -0400
  Re: Running a command line program and reading the result as it runs Peter Otten <__peter__@web.de> - 2013-08-23 18:39 +0200

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