[bip] replacing those shell scripts ... the PipeChain

[James Casbon]

So I often want to use the unix toolchain to get a quick idea of some
data.  You know, grep this, cut that, sort, etc.  I often find myself
thinking that I won't use python because writing all those Popen(blah,
stdout=PIPE) is just too verbose.  However, this means that the
migration from shell script to python script has an annoying little
little bump.

So, without further ado, I present a little helper called PipeChain.
This allows this kind of code:

chain = PipeChain('grep ^x', 'cut -d" " -f2-3', 'sort', 'uniq -c')

# use on a file
proc = chain(file('input1.txt), file('output1.txt'))
proc.wait()

# or get a handle on the results
proc = chain(file('input1.txt))
proc.stdout.read()


I have attached the file. I need one bit of help though - it would be
nice to be able to pass in an iterable to use as the input_handle.
subprocess either wants a proper handle, or PIPE.  How can you stream
an iterable into a subprocess.PIPE without blocking?

cheers,
James
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