On 2009-09-30 11:38 AM, Guido van Rossum wrote:
On a tangent -- a use case that I see happening frequently but which
is pretty poorly supported by optparse is a command-line that has a
bunch of general flags, then a 'subcommand name', and then more flags,
specific to the subcommand. Most here are probably familiar with this
pattern from SVN, Hg, and other revision control systems (P4 anyone?)
with a rich command-line interface. There are some variants, e.g.
whether global and subcommand-specific flags may overlap, and whether
flags may follow positional args (Hg and SVN seem to differ here a
bit).
I've helped write at least two tools at Google that have this
structure; both used different approaches, and neither was
particularly easy to get right. Getting all the different --help
output to make sense was mostly a manual process. (E.g. "foo --help"
should print the general flags and the list of known subcommands,
whereas "foo --help subcommand" should print flags and other usage
info about the specific subcommand.) Also switching out to different
calls based on the subcommand should/might be part of this.
I would be willing to live with a third option parser in the stdlib if
it solved this problem well.
I don't think argparse supports the "foo --help subcommand" OOB. I think it
would be simple to modify argparse to make it do so. It does support general
options followed by a subcommand with options, though.
http://argparse.googlecode.com/svn/tags/r101/doc/other-methods.html#sub-commands
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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