Ian Simcock <ian.simc...@internode.on.net> writes:
> Greetings all.
>
> I'm using Python 2.7 under Windows and am trying to run a command line
> program and process the programs output as it is running. A number of
> web searches have indicated that the following code would work.
>
> import subprocess
>
> p = subprocess.Popen("D:\Python\Python27\Scripts\pip.exe list -o",
> stdout=subprocess.PIPE,
> stderr=subprocess.STDOUT,
> bufsize=1,
> universal_newlines=True,
> shell=False)
> for line in p.stdout:
> print line
>
> When I use this code I can see that the Popen works, any code between
> the Popen and the for will run straight away, but as soon as it gets
> to the for and tries to read p.stdout the code blocks until the
> command line program completes, then all of the lines are returned.
>
> Does anyone know how to get the results of the program without it blocking?
When file object is used in a for loop it works like an iterator
and then it uses a hidden read-ahead buffer.
It might cause this kind of blocking.
You can read more details here (description of method ``next``):
http://docs.python.org/lib/bltin-file-objects.html
So basically non-blocking loop might look like this:
while True:
line = p.stdout.readline()
if not line: break
print line
HTH,
Rob
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