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

[Ian Simcock]

Rob Wolfe wrote:
> Ian Simcock <Ian.Simcock at Internode.on.net> writes:
>
> 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
>

Thanks, but some further research seems to indicate that the problem is 
that the standard C libraries are probably buffering the output when the 
it's being redirected, so the problem is coming from the command line 
tool rather than the python code.

Ian Simcock.