Re: [PATCH] Replace git-cvsimport with a rewrite that fixes major bugs.

From: Michael Haggerty <mhagger@alum.mit.edu>
Date: Jan 3, 2013, 16:24 UTC
Message-ID: <50E5B0B2.7060205@alum.mit.edu>
In-Reply-To: <7vip7expd8.fsf@alter.siamese.dyndns.org>

On 01/03/2013 04:22 PM, Junio C Hamano wrote:

Show 7 quoted lines

> Antoine Pelisse <apelisse@gmail.com> writes:
> 
>>> Doesn't Python come with a standard subprocess module that lets you
>>> spawn external programs safely, similar to the way Perl's list form
>>> open(), e.g. "open($fh, "-|", 'git', @args)", works?
> 
> ... and of course a more boring "system('git', $subcmd, @args)", as well.

Python's os.system() takes exactly one argument, which must be a string, and executes it in a subshell. subprocess is indeed the way to go.

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>> You mean something like this:
>>
>>   p1 = subprocess.Popen([backend.command()], stdout=subprocess.PIPE)
>>   subprocess.Popen(["git", "fast-import", "--quiet"] + gitopts,
>> cwd=outdir, stdin=p1.stdout)
>>
>> Assuming gitopts is a list rather than a string. (care must be taken
>> with backend.command() also)
> 
> Yes.
> 
> I vaguely recall that the subprocess module once used to be one
> portability issue but that was between Python 2.3 and 2.4 or some
> ancient history, and it should no longer be relevant.

subprocess was added in Python 2.4, and the above example should work fine in any version >= 2.4. But please note that other functions have been added to the module since then, like check_call() (v2.5), check_output (v2.7), and some methods were added to the Popen object in v2.6.

Such things are documented pretty reliably in the Python library documentation [1]; when in doubt, one can view older versions of the library documentation, which are all available online [2].

Michael

[1] http://docs.python.org/2/library/ [2] http://www.python.org/doc/versions/

-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/