better way for ' '.join(args) + '\n'?

[Prasad, Ramit]

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.
> 
> Stop.
> 
> 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([
> 		"'"+st.replace("'","'\\''")+"'"
> 		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.

>>> a
('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\''


Ramit Prasad


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