better way for ' '.join(args) + '\n'?
ramit.prasad at jpmorgan.com
Mon Oct 29 23:28:52 CET 2012
Thomas Rachel wrote:
> Am 26.10.2012 09:49 schrieb Ulrich Eckhardt:
> > Hi!
> > General advise when assembling strings is to not concatenate them
> > repeatedly but instead use string's join() function, because it avoids
> > repeated reallocations and is at least as expressive as any alternative.
> > What I have now is a case where I'm assembling lines of text for driving
> > a program with a commandline interface.
> In this case, you think too complicated.
> Just do
> subprocess.Popen(['prog', 'foo', 'bar', 'baz'])
> - is the most safest thing for this use case.
> If it should not be possible for any reason, you should be aware of any
> traps you could catch - e.g., if you want to feed your string to a
> Bourne shell, you should escape the strings properly.
> In such cases, I use
> def shellquote(*strs):
> r"""Input: file names, output: ''-enclosed strings where every ' is
> replaced with '\''. Intended for usage with the shell."""
> # just take over everything except ';
> # replace ' with '\''
> # The shell sees ''' as ''\'''\'''\'''. Ugly, but works.
> return " ".join([
> for st in strs
> so I can use
> shellquote('program name', 'argu"ment 1', '$arg 2',
> "even args containing a ' are ok")
> For Windows, you'll have to modify this somehow.
The subprocess module suggests using pipes.quote for escaping.
('program name', 'argu"ment 1', '$arg 2', "even args containing a ' are ok")
>>> import pipes
>>> map(pipes.quote, a)
["'program name'", '\'argu"ment 1\'', "'$arg 2'", '\'even args containing a \'"\'"\' are ok\'']
>>> ' '.join(a)
'\'program name\' \'argu"ment 1\' \'$arg 2\' \'even args containing a \'\\\'\' are ok\''
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