Nick Coghlan <[email protected]> added the comment:
It's a flow thing. This idea was kicked off by the process of translating a
large Perl script to Python and paying attention to what the translation made
*worse*.
One of the big things it made worse was the translation of "qx" (quoted
executable) strings. In Perl, those are almost as neat and tidy as if you were
writing directly in the shell:
qx|ls -l $dirname|
The thought process isn't "build this command and then execute it", it's "run
this shell command".
Yes, you have to be careful that "dirname" is legal in the shell, but that
usually isn't a big problem in practice, because dirname came from a previous
listdir call, or you otherwise know that it's valid to interpolate it into the
command (and if it isn't, then the bug lies in the way 'dirname' was populated,
not in this operation).
Now, Python's never going to have implicit string interpolation, and that's
fine - we have explicit interpolation instead. A direct translation of the
above to idiomatic Python 2.7 code looks like the following:
subprocess.check_output("ls -l {}".format(dirname), shell=True)
Now, if I'm doing system administration tasks (like the script I was
translating), then I'm going to be doing that kind of thing a *lot*. I'm also
likely to be a sysadmin rather than a programmer, so rather than going "Oh, I
can write a helper function for this", my natural reaction is going to be "I'm
going to use a language that doesn't get in my way so much".
This proposal is aimed directly at making Python a better language for systems
administration by making shell invocation almost as easy as it is in Perl:
shutil.check_shell_output("ls -l {}", dirname)
Heck, if someone really wanted to, they could even do:
qx = shutil.check_shell_output
qx("ls -l {}", dirname)
However, this is also why I *don't* want these methods in subprocess - they put
the burden on the user to think about their data as if they were writing shell
scripts, because that data is going to get passed straight to the shell for
execution without any additional escaping. That's a reasonable idea for a shell
utility in shutil, it's not reasonable for a general purpose subprocess
manipulation utility in subprocess.
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<http://bugs.python.org/issue13238>
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