I'm using Python's optparse to do what it does best, but I can't figure out how to make the option callback trigger on the default argument value if no other is specified via command-line; is this even possible? This would make my code much cleaner.
I can't use argparse unfortunately, as the platform I'm running on has an outdated Python version.
Edit: To provide more detail, I'm adding an option with a callback and a default value
parser.add_option(
"-f",
"--format",
type = "string",
action = "callback",
callback = format_callback,
default = "a,b,c,d")
The callback function is defined as follows:
def format_callback(option, opt, value, parser):
# some processing
parser.values.V = processed_value
Basically I'm processing the "--format" value and putting the result into the parser. This works fine, when "--format" is specified directly via command-line, but I'd like the callback to be triggered on the default "a,b,c,d" value as well.
It is simply not possible.
The optparse.OptionParser implementation of parse_args starts with:
def parse_args(self, args=None, values=None):
"""
parse_args(args : [string] = sys.argv[1:],
values : Values = None)
-> (values : Values, args : [string])
Parse the command-line options found in 'args' (default:
sys.argv[1:]). Any errors result in a call to 'error()', which
by default prints the usage message to stderr and calls
sys.exit() with an error message. On success returns a pair
(values, args) where 'values' is an Values instance (with all
your option values) and 'args' is the list of arguments left
over after parsing options.
"""
rargs = self._get_args(args)
if values is None:
values = self.get_default_values()
Default values are set before processing any arguments. Actual values then overwrite defaults as options are parsed; the option callbacks are called when a corresponding argument is found.
So callbacks simply cannot be invoked for defaults. The design of the optparse module makes this very hard to change.