Peter Otten wrote:
Ian Simcock wrote:
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?
The following works on my linux system:
import subprocess
p = subprocess.Popen(
["ping", "google.com"],
stdout=subprocess.PIPE)
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.
Hmm... and so it comes full circle.
I thought that the inclusion of the iter call looked familiar so I
checked my original code and found that it was there. I removed it when
shrinking the code down to a minimal example for posting. Then, after
removing it, which triggered the blocking, I changed the command to ping
so that it's easier for anyone to test.
I've tried a copy of my original code using the ping command and it
works fine.
So it looks like the python package manager pip must see that it's not
going to a console and buffer the output, and my original code was not
the problem.
So I can't do what I want, but it's interesting to know that for some
reason the iter is required for the occasions when it can work.
Thanks to everyone who helped with this.
Ian Simcock
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