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Groups > comp.lang.python > #90845

Why does the first loop go wrong with Python3

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I have the following code:
    from __future__     import division, print_function

    import subprocess

    p = subprocess.Popen('ls -l', shell = True, stdout = subprocess.PIPE)
    for line in iter(p.stdout.readline, ''):
        print(line.rstrip().decode('utf-8'))

    p = subprocess.Popen('ls -l', shell = True, stdout = subprocess.PIPE)
    for line in p.stdout.readlines():
        print(line.rstrip().decode('utf-8'))

This works in Python2. (Both give the same output.)

But when I execute this in Python3, then the first loop is stuck in a
loop where it continually prints a empty string. The second loop is
executed correctly in Python3.

In the current case it is not a problem for me, but when the output
becomes big, the second solution will need more memory. How can I get
the first version working in Python3?

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof

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Thread

Why does the first loop go wrong with Python3 Cecil Westerhof <Cecil@decebal.nl> - 2015-05-19 14:24 +0200
  Re: Why does the first loop go wrong with Python3 Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-19 14:16 +0100
    Re: Why does the first loop go wrong with Python3 Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2015-05-19 16:38 +0200
    Re: Why does the first loop go wrong with Python3 Cecil Westerhof <Cecil@decebal.nl> - 2015-05-19 16:44 +0200
      Re: Why does the first loop go wrong with Python3 Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-19 09:49 -0600
        Re: Why does the first loop go wrong with Python3 Cecil Westerhof <Cecil@decebal.nl> - 2015-05-19 18:39 +0200
          Re: Why does the first loop go wrong with Python3 Chris Angelico <rosuav@gmail.com> - 2015-05-20 03:11 +1000

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