> @andersk: Would the restriction to only having flags with a fixed
> number of arguments be acceptable for your use case?

I think that’s fine.  Anyone coming from optparse won’t need options with optional arguments.

However, FWIW, GNU getopt_long() supports options with an optional argument under the restrictions that:
 • the option must be a long option,
 • the optional argument must be the only argument for the option, and
 • the argument, if present, must be supplied using the
   ‘--option=argument’ form, not the ‘--option argument’ form.
This avoids all parsing ambiguity.  It would be useful to have feature parity with getopt_long(), to facilitate writing Python wrapper scripts for C programs.