homepage

I think that optparse is doing the right thing here. I think that your code example should be changed to:
import optparse
 parser = optparse.OptionParser()
 parser.add_option("-o", "--option", action = "append")
 options, args = parser.parse_args()
 if not options.option:
 options.option = ['a']
 print options
Think of the default as the initial list, and each time the -o option is specified, an item is appended to that initial list.