how to simulate tar filename substitution across piped subprocess.Popen() calls?

[jkn]

slight followup ...

I have made some progress; for now I'm using subprocess.communicate to
read the output from the first subprocess, then writing it into the
secodn subprocess. This way I at least get to see what is
happening ...

The reason 'we' weren't seeing any output from the second call (the
'xargs') is that as mentioned I had simplified this. The actual shell
command was more like (in python-speak):

"xargs -I {} sh -c \"test -f %s/{} && md5sum %s/{}\"" % (mydir, mydir)

ie. I am running md5sum on each tar-file entry which passes the 'is
this a file' test.

My next problem; how to translate the command-string clause

    "test -f %s/{} && md5sum %s/{}" # ...

into s parameter to subprocss.Popen(). I think it's the command
chaining '&&' which is tripping me up...

    Cheers
    J^n