using python variables inside quotes

[Jeff Collins]

lewst writes:
 > Greetings,
 > 
 > This is a simple question, so please excuse, but I am slowly learning
 > Python by trying to rewrite all my Perl scripts.  Thus far I like it
 > much better than Perl, but a small matter has me stumped.
 > 
 > My question deals with using variables inside quotes.  Take this
 > sample program for example:
 > 
 >   #!/usr/bin/env python
 > 
 >   import os, random
 > 
 >   imgdir = "/home/lewst/images/"

For sake of portability, you may wish to write:
     imgdir = os.path.join("home","lewst","images")

 >   piclist = os.listdir(imgdir)
 > 
 >   chosenpic = imgdir + random.choice(piclist) 

     chosenpic = os.path.join(imgdir, random.choice(piclist))

 >   os.system("xv %s &" % chosenpic)

I tend to like this better than the perl way.  When you become more
acustomed to python, the concept of embedding variables in a string
just won't seem natural.

Other possibilities:

1)
     os.system(string.join(("xv", chosenpic, "&")))

2) <more complex and ugly, but provides a perl flavor>

     os.system("xv %(chosenpic)s &" % locals())

3) custom function
     def xv(pic):
        os.system('xv %s &' % pic)

     xv(chosenpic)

 > 
 > This script displays a random image from a directory full of images
 > using the "xv" image manipulation program.  
 > 
 > Is there a simpler way to access the `chosenpic' variable within the
 > os.system() call?  At first I tried the following:
 > 
 >   os.system("xv chosenpic &")
 > 
 > This didn't work, because it is looking for the literal "chosenpic"
 > instead of the name of one of my images.
 > 
 > In Perl, I could use the following:
 > 
 >   system("xv $chosenpic &");
 > 
 > Perl recognizes the `$' as a variable.  Since in Python variables are
 > not declared with punctuation marks like this, it is not as easy to
 > distinguish them from regular words.
 > 
 > Have I missed something trivial?  
 > 
 > (Please CC: me on followups)
 > 
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