On 2012-09-13 16:34, Jean-Michel Pichavant wrote:
----- Original Message -----
I have a subprocess.call which tries to download a data from a remote
server using HTAR. I put the call in a while loop, which tests to
see if the download was successful, and if not, loops back around up
to five times, just in case my internet connection has a hiccup.
Subprocess.call is supposed to wait.
But it doesn't work as intended. The loop quickly runs 5 times,
starting a new htar command each time. After five times around, my
program tells me my download failed, because the target file doesn't
yet exist. But it turns out that the download is still
happening---five times.
When I run htar from the shell, I don't get a shell prompt again
until after the download is complete. How come control is returned
to python before the htar command is through?
I've tried using Popen with wait and/or communicate, but no waiting
ever happens. This is troublesome not only because I don't get to
post process my data, but because when I run this script for
multiple datasets (checking to see whether I have local copies), I
quickly get a "Too many open files" error. (I began working on that
by trying to use Popopen with fds_close, etc.)
Should I just go back to os.system?
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A related subset of code would be useful.
You can use subprocess.PIPE to redirect stdout & stderr et get them with
communicate, something like:
proc = subprocess.Popen(['whatever'], stdout=subprocess.PIPE,
stdout=subprocess.PIPE)
stdout, stderr = proc.communicate()
print stdout
print stderr
Just by looking at stdout and stderr, you should be able to see why htar is
returning so fast.
JM
PS : if you see nothing wrong, is it possible that htar runs asynchronously ?
The OP says that it waits when run from the shell.
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