On 2/15/2010 7:35 AM, R (Chandra) Chandrasekhar wrote:
Dear Folks,
I want to execute a command from within python using the subprocess module.
Coming from a Perl background, I thought I could use variable
interpolation in strings, but found that this is neither supported
Yes, it is: see the use of string.Template below.
... nor
the Python way.
That right -- it isn't the Python way. Python offers two basic
alternatives. Alf already presented the use of the "new" format() method
of string objects. I think "traditional" Python string formatting might
be what you want in this case:
colors = ['#abcdef', '#456789']
format_string = "convert -size 5x30 gradient:%s-%s /tmp/image.png"
cmd_string = format_string % tuple(colors)
... or better, by making *colors* a tuple instead of a list ...
colors = ('#abcdef', '#456789')
format_string = "convert -size 5x30 gradient:%s-%s /tmp/image.png"
cmd_string = format_string % colors
As Peter demonstrated, you need to use split() on *cmd_string* when you
send the command to subprocess.call().
Now if you *really* miss using Perl, try this:
c1, c2 = ('#abcdef', '#456789')
template = string.Template(
"convert -size 5x30 gradient:$c1-$c2 /tmp/image.png")
cmd_string = template.substitute(locals())
Not worth the trouble, IMHO.
Refs:
http://www.python.org/doc/2.5.2/lib/typesseq-strings.html
http://www.python.org/doc/2.5.2/lib/node40.html
HTH,
John
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