Executing a command from within python using the subprocess module

Steve Holden steve at holdenweb.com
Mon Feb 15 17:31:58 CET 2010


R (Chandra) Chandrasekhar wrote:
> Peter Otten wrote:
>> import subprocess
>>
>> def convert(width=5, height=30, colors=['#abcdef', '#456789'],
>>             filename="tmp/image with space in its name.png"):
>>     lookup = locals()
>>     assert all("\n" not in str(s) for s in lookup.values())
>>     subprocess.call("""\
>> convert
>> -size
>> {width}x{height}
>> gradient:{colors[0]}-{colors[1]}
>> {filename}""".format(**lookup).splitlines())
>>
>> convert()
>>
>> Peter
> 
> One other question I forgot to ask is this why is there a terminal
> backslash in
> 
>> subprocess.call("""\
> 
> Removing the backslash makes the function fail.
> 
> I wonder why, because """ is supposed to allow multi-line strings. I am
> sorry if this sounds obtuse but that backslash baffles me.

It does, but a leading newline would cause the splitlines() result to
start with an empty word - the backslash just causes the interpreter to
ignore the newline immediately following, rather than including it in
the string literal's value.

regards
 Steve
-- 
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