[Tutor] NEWBIE!! pipes
Thu, 1 Feb 2001 11:22:49 -0700 (MST)
On Wed, 31 Jan 2001 AquaRock7@aol.com wrote:
> What are pipes? The docs barely touched this subject, it assumed you already
> knew what they are... From context I am gathering that it is a connection to
> the kernel? (maybe?) How can I utilize this?
A "pipe" is a connection between two programs, from the stdout of one to
the stdin of another. On a unix command line you would write it as:
prog1 | prog2 | prog3
Which would pipe the output of prog1 to the input prog2, etc.
> 1 more quickie:
> >if __name__ == '__main__':
> > main()
> what is the pourpose if the above code? It runs the sub main() (duh :) but,
> why not just main() wihtout the if? what is the conditional testing for?
> and what are the variables __main__ and __name__? i dont believe they are
> defined in the program, so just what are they? and, what does putting "__"
> around a variable actually DO besides look cool ?
Ya, cool, until you try to read it done in a proportional font and can't
tell how many underscores are present. anyways...
When Python is executing the mainline of a program __name__ has the
value "__main__", so, the above snippet would only execute the main()
routine if the code was being executed as part of the mainline of a
program. i.e., doing "python snippet" would execute main(), doing
"import snippet" from within a Python program would not. It tends to
be used it like this...
----- module: snip2
# class and function test routine
if __name__ == "__main__":
When I want to test what I'm woring on I do "^C^C" to execute the
buffer, __name__ == "__main__" and the test code is run; when a prg
imports the finished module the test code is ignored. The prog doing
the importing could also do a "snip2.main()" to run the test code.