Dean Troyer fbc412e533 Multiple API version support

* Use multiple entry point groups to represent each API+version
  combination supported
* Add some tests

Try it out:
* Right now only '* user' commands have multiple overlapping versions;
  you can see the selection between v2.0 and v3 by looking at the
  command help output for 'tenant' vs 'project':

  os --os-identity-api-version=2.0 help set user
  os --os-identity-api-version=3 help set user

Change-Id: I7114fd246843df0243d354a7cce697810bb7de62

2013-02-06 11:36:28 -06:00

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Commands

Command Structure

OpenStack Client uses a command form verb object.

Note that 'object' here refers to the target of a command's action. In coding discussions 'object' has its usual Python meaning. Go figure.

Commands take the form:

openstack [<global-options>] <verb> <object> [<command-local-arguments>]

Command Arguments

All long option names use two dashes ('--') as the prefix and a single dash ('-') as the interpolation character. Some common options also have the traditional single letter name prefixed by a single dash ('-').

Global options generally have a corresponding environment variable that may also be used to set the value. If both are present, the command-line option takes priority. The environment variable names can be derived from the option name by dropping the leading '--', converting all embedded dashes ('-') to underscores ('_'), and converting the name to upper case.

Positional arguments trail command options. In commands that require two or more objects be acted upon, such as 'attach A to B', both objects appear as positional arguments. If they also appear in the command object they are in the same order.

Implementation

The command structure is designed to support seamless addition of extension command modules via entry points. The extensions are assumed to be subclasses of Cliff's command.Command object.

Command Entry Points

Commands are added to the client using distribute's entry points in setup.py. There is a single common group openstack.cli for commands that are not versioned, and a group for each combination of OpenStack API and version that is supported. For example, to support Identity API v3 there is a group called openstack.identity.v3 that contains the individual commands. The command entry points have the form:

"verb_object=fully.qualified.module.vXX.object:VerbObject"

For example, the 'list user' command fir the Identity API is identified in setup.py with:

'openstack.identity.v3': [
    # ...
    'list_user=openstackclient.identity.v3.user:ListUser',
    # ...
],

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