os.shell, recursion, encryption

55555 55555 at dakotacom.net
Sat Jun 2 09:17:52 CEST 2012

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Date: 14 Feb 2000 20:08:32 -0600
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Thanks for the lesson.  It's a little clearer, but now I question whether 
this can be used for what I want to do.  It seems like popen creates a 
file.  I don't want to do that.  Instead, I'd like to simply run a 
commercial program with a command like 'pkzip asdf.zip *.*'.  I gave the 
following a try and it came back with "bad command or filename."  Am I on 
the right path or should I be using a different function than popen?  
os.system() doesn't work and I don't know what mode to use for spawnv.  
Thanks again.

import os
os.popen('> '+zipExe+' asdf.zip *.*', 'w')

On Mon, 14 Feb 2000 20:44:45 GMT, wware at world.std.com (Will Ware) wrote:
> 55555 (55555 at dakotacom.net) wrote:
> : How does os.popen work?  I'm afraid that I don't understand pipes.
> Caveat: I'm a Unix guy, pretty clueless about Windows, and this may
> all be Unix-ish stuff.
> When you open a file for reading, the file becomes a source of bytes.
> You read the bytes in sequence and there is some testable condition
> to tell you when there are no more bytes. Since many files are text,
> it's often convenient to take the bytes in lines. So you often see
> idioms like this:
> f = open('somefile')
> for L in f.readlines():
> 	.... do something with L ....
> f.close()
> or more tersely:
> for L in open('somefile').readliines():
> 	.... do something with L ....
> In this latter case, the opened file should automatically be closed
> when it gets garbage-collected. (Whether that happens, or the
> conditions under which it might not, is another question for subtler
> minds than mine.)
> In Unix, many programs (particularly ones that operate on text) are
> written to look like filters, meaning that they accept a stream of
> bytes from elsewhere and produce a stream of bytes that can go to
> yet somewhere else. Each such program has "standard input" and
> "standard output". Output from one program can be directed to the
> input of another, and hence the term "pipe", just like in plumbing.
> So you see constructs like this:
>    filter1 < infile | filter2 | filter3 | filter4 > outfile
> And this means that the contents of 'infile' are run thru all four
> filters in succession, and the results end up in 'outfile'.
> Python, too, can accept input from a chain of filters, so I can
> type something like this:
> p = os.popen('filter1 < infile | filter2 | filter3 | filter4')
> for L in p.readlines():
> 	... do stuff with L ...
> p.close()
> and this means that I want, as input, the stuff that would have
> been dumped into 'outfile' in the earlier example.
> Sorry if this seems circuitous and long-winded (and I'm _really_
> sorry if none of this is meaningful in the Windows world), but this
> saves you the hassle of creating a bunch of intermediate files to
> catch the output at each stage in the pipeline. (Essentially Unix
> is creating those files itself and keeping track of them without
> bothering you with the details, and they all disappear when you're
> finished.)
> I suspect Python would also be happy with an output pipe, something
> where you'd be writing to the front of a pipeline like this:
> p = os.popen('filter1 | filter2 | filter3 | filter4 > outfile', 'w')
> for <some loop>:
> 	...
> 	p.write(....)
> p.close()
> but I've never myself written that, that I can recall.
> -- 
> -- I can picture in my mind a world without war, a world without hate. 
And --
> -- I can picture us attacking that world, because they'd never expect 
it.  --
> Will Ware - N1IBT - wware at world.std.com

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