python optparse mini tutorial / how to

Here's a little tutorial on how to use the optparse module in the Python standard library.

1. So far I've only been using optparse.OptionParser so I do the
   following:
   
   

   
       from optparse import OptionParser
   

   
   


2. Define a usage string. I've been using:
   
   

   
       usage = "Usage: %prog [options]"
   

   
   
3. Define a parser: parser = OptionParser( usage = usage )


4. Set the defaults: parser.set_defaults( somevar = defaultvalue )


5. Add options:
   
   
   
   1. Example of command line options that have arguments:
      
      

      
          parser.add_option(
                "--someopt",
                action="store",
                dest="someoptname",
                help="help info for --someopt" )
      

      
      
   
   
   2. Example of command line option that acts as a switch/toggle:
      
      

      
          parser.add_option(
                "--turniton",
                action="store_true",
                dest"turnitonflag",
                help="help for turniton" )
      

      
      
   
   
   3. Another useful argument is metavar - helps you to name the variable being addressed by the option. The default is ok.
   
   
   
   


6. Get the options and arguments:
   
   

   
       (options, args) = parser.parse_args()
   

   
   


7. At this point it all depends on what you want to do. Let's say we want to access the options defined above:
   
   
   
   • To access someoptname:
     
     

     
          someoptname = options.someoptname
     

     
     
   
   
   • To access turnitonflag and store in a differently named variable:
     
     

     
          myturnitonflag = options.turnitonflag
     

     
     
   
   
   • You get the picture.
   
   
   
   
8. You can use parser.error( "some message to indicate what went wrong" ) to convey to user that the options didn't work.

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