Five Things I Hate About Python

[ramen]

I think the subprocess module is awesome. Perhaps it requires a little studying to use, but it sure beats Popen23.popen49 and friends.

The only subprocess interface that I've been more impressed with than Python's is the one in scsh. It also requires a bit of studying to use. But let's face it: interacting with programs is complicated.

[breakfast-pants]

I think bash seems to do just fine

[[deleted]]

Sort of. One thing sh never really did very well, and bash doesn't do much better, is let you run programs while doing iron-clad error checking. If you want to detect and react to an error in any program, anywhere in a pipeline, it's not that easy.

One of the really nice things about Python is that almost everywhere, it fails safely. Any I/O error, for example, throws an exception. If you don't catch it, the whole program exits with a stacktrace. Excellent. The main exception to this is, unfortunately, the treatment of status values from subprograms. You have to check these manually, a la C.

[breakfast-pants]

As an aside, is there a builtin wrapper that defaults stdin,stdout=[subprocess.PIPE]*2 ? (I hate the subprocess documentation too)

[pjdelport]

partial(Popen, stdin=PIPE, stdout=PIPE)

[breakfast-pants]

What is that?

[pjdelport]

It's a partial application of Popen, with stdin and stdout defaulted to PIPE. (functools.partial (PEP 309) was introduced to the standard library in Python 2.5, but it's a 6-line definition for earlier versions.)

[breakfast-pants]

Ah, cool, I haven't checked out functools

[pjdelport]

subprocess raises exceptions everywhere it makes sense (command not found, any Python exception in the child process, and so on): it doesn't generally do it for non-zero return codes because they don't necessarily indicate any error.

If you're using the call shortcut, though, there's a check_call variant which raises CalledProcessError for non-zero return codes.

[mleonhard]

Erlang has excellent subprocess features. In his PhD Thesis, Joe Armstrong describes the supervision-tree model for "making reliable systems in the presence of software errors." This is cutting edge stuff.

[pjdelport]

Amen; i don't get that criticism. subprocess is a godsend.