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Re: Popen and reading stdout in windows

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  Re: Popen and reading stdout in windows Dave Angel <davea@davea.name> - 2013-06-10 15:46 -0400

#47593 — Re: Popen and reading stdout in windows

On 06/10/2013 02:37 PM, Joseph L. Casale wrote:
> I have a use where writing an interim file is not convenient and I was hoping to
> iterate through maybe 100k lines of output by a process as its generated or
> roughly anyways.
>
> Seems to be a common question on ST, and more easily solved in Linux.
> Anyone currently doing this with Python 2.7 in windows and can share some
> guidance?
>

You leave out an awful amount of detail.  I have no idea what ST is, so 
I'll have to guess your real problem.

You've got a process (myprog.exe) which generates a medium amount of 
output to stdout, and you want to process that data in a python program 
as it's being output, but without first writing it to a file.

If by process you meant grep, the answer would be as simple as

myprocess | grep  parm1 parm2

But you want to write something (not called grep) in Python.

myprocess | python myfilter.py

The question is how to write myfilter.py


Answer is to use stdin as you would a file.  it's already open for you, 
and it'll get the data as it's being generated (plus or minus some 
buffering).  So you can simply do something like:



import sys
for index, line in enumerate(sys.stdin):
     print index, line


This trivial "filter" adds a line number in front of every line.  But 
you could do anything there.  And you might not need enumerate if you 
don't care about the line number.

-- 
DaveA

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