Re: Weird error handling in os._execvpe
Hello, I think the patch associated with this thread has an unintended consequence. In http://mail.python.org/pipermail/python-dev/2002-August/027229.html Zack pointed out three flaws in the original code: [...] Third, if an error other than the expected one comes back, the loop clobbers the saved exception info and keeps going. Consider the situation where PATH=/bin:/usr/bin, /bin/foobar exists but is not executable by the invoking user, and /usr/bin/foobar does not exist. The exception thrown will be 'No such file or directory', not the expected 'Permission denied'. The patch, as I understand it, changes the behaviour so as to raise the exception "Permission denied" in this case. Consider a similar situation in which both /bin/foobar (not executable by the user) and /usr/bin/foobar (executable by the user) exist. Given the command "foobar", the shell will execute /usr/bin/foobar. If I understand the patch correctly, python will give up when it encounters /bin/foobar and raise the "Permission denied" exception. I believe this just happened to me today. I had a shell script named "gcc" in ~/bin (first on my path) some months back. When I was finished with it, I just did "chmod -x ~/bin/gcc" and forgot about it. Today was the first time since this patch went in that I ran gcc via python (using scipy's weave). Boy was I surprised at the message "unable to execute gcc: Permission denied"! I guess the fix is to save the EPERM exception and keep going in case there is an executable later in the path. Regards, -Steve
I think the patch associated with this thread has an unintended consequence.
In http://mail.python.org/pipermail/python-dev/2002-August/027229.html Zack pointed out three flaws in the original code:
[...] Third, if an error other than the expected one comes back, the loop clobbers the saved exception info and keeps going. Consider the situation where PATH=/bin:/usr/bin, /bin/foobar exists but is not executable by the invoking user, and /usr/bin/foobar does not exist. The exception thrown will be 'No such file or directory', not the expected 'Permission denied'.
The patch, as I understand it, changes the behaviour so as to raise the exception "Permission denied" in this case.
Consider a similar situation in which both /bin/foobar (not executable by the user) and /usr/bin/foobar (executable by the user) exist. Given the command "foobar", the shell will execute /usr/bin/foobar. If I understand the patch correctly, python will give up when it encounters /bin/foobar and raise the "Permission denied" exception.
I believe this just happened to me today. I had a shell script named "gcc" in ~/bin (first on my path) some months back. When I was finished with it, I just did "chmod -x ~/bin/gcc" and forgot about it. Today was the first time since this patch went in that I ran gcc via python (using scipy's weave). Boy was I surprised at the message "unable to execute gcc: Permission denied"!
I guess the fix is to save the EPERM exception and keep going in case there is an executable later in the path.
This is definitely a bug. Can you or Zack provide a patch? I've opened a bug report: http://python.org/sf/601077 --Guido van Rossum (home page: http://www.python.org/~guido/)
participants (2)
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Guido van Rossum
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Steve M. Robbins