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Python Library Reference |  |
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Things get hairy when you want an option to take a variable number of
arguments. For this case, you must write a callback, as optparse doesn't
provide any built-in capabilities for it. And you have to deal with
certain intricacies of conventional Unix command-line parsing that optparse
normally handles for you. In particular, callbacks should implement
the conventional rules for bare "-" and "-" arguments:
"-" or "-" can be option arguments
"-" (if not the argument to some option): halt command-line
processing and discard the "-"
"-" (if not the argument to some option): halt command-line
processing but keep the "-" (append it to parser.largs)
If you want an option that takes a variable number of arguments, there are several subtle, tricky issues to worry about. The exact implementation you choose will be based on which trade-offs you're willing to make for your application (which is why optparse doesn't support this sort of thing directly).
Nevertheless, here's a stab at a callback for an option with variable arguments:
def vararg_callback(option, opt_str, value, parser):
assert value is None
done = 0
value = []
rargs = parser.rargs
while rargs:
arg = rargs[0]
# Stop if we hit an arg like "--foo", "-a", "-fx", "--file=f",
# etc. Note that this also stops on "-3" or "-3.0", so if
# your option takes numeric values, you will need to handle
# this.
if ((arg[:2] == "--" and len(arg) > 2) or
(arg[:1] == "-" and len(arg) > 1 and arg[1] != "-")):
break
else:
value.append(arg)
del rargs[0]
setattr(parser.values, option.dest, value)
[...]
parser.add_option("-c", "--callback",
action="callback", callback=varargs)
The main weakness with this particular implementation is that negative
numbers in the arguments following "-c" will be interpreted as
further options (probably causing an error), rather than as arguments to
"-c". Fixing this is left as an exercise for the reader.
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Python Library Reference | |
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