python-openstackclient/doc/source/command-options.rst

Command Options

OpenStackClient commands all have a set of zero or more options unique to the command, however there are of course ways in which these options are common and consistent across all of the commands that include them.

These are the set of guidelines for OSC developers that help keep the interface and commands consistent.

In some cases (like the boolean variables below) we use the same pattern for defining and using options in all situations. The alternative of only using it when necessary leads to errors when copy-n-paste is used for a new command without understanding why or why not that instance is correct.

The Human Interface Guide <humaninterfaceguide> describes the guildelines for option names and usage. In short: * All option names shall be GNU-style long names (two leading dashes). * Some global options may have short names, generally limited to those defined in support libraries such as cliff.

General Command Options

Boolean Options

Boolean options for any command that sets a resource state, such as 'enabled' or 'public', shall always have both positive and negative options defined. The names of those options shall either be a naturally occurring pair of words (in English) or a positive option and a negative option with no- prepended (such as in the traditional GNU option usage) like --share and --no-share.

In order to handle those APIs that behave differently when a field is set to None and when the field is not present in a passed argument list or dict, each of the boolean options shall set its own variable to True as part of a mutually exclusive group, rather than the more common configuration of setting a single destination variable True or False directly. This allows us to detect the situation when neither option is present (both variables will be False) and act accordingly for those APIs where this matters.

This also requires that each of the boolean values be tested in the take_action() method to correctly set (or not) the underlying API field values.

--enable

Enable <resource> (default)

--disable

Disable <resource>

Implementation

The parser declaration should look like this:

enable_group = parser.add_mutually_exclusive_group()
enable_group.add_argument(
    '--enable',
    action='store_true',
    help=_('Enable <resource> (default)'),
)
enable_group.add_argument(
    '--disable',
    action='store_true',
    help=_('Disable <resource>'),
)

An example handler in `take_action()`:

# This leaves 'enabled' undefined if neither option is present
if parsed_args.enable:
    kwargs['enabled'] = True
if parsed_args.disable:
    kwargs['enabled'] = False

Options with Choices

Some options have a specific set of values (or choices) that are valid. These choices may be validated by the CLI. If the underlying API is stable and the list of choices are unlikely to change then the CLI may validate the choices. Otherwise, the CLI must defer validation of the choices to the API. If the option has a default choice then it must be documented.

Having the CLI validate choices will be faster and may provide a better error message for the user if an invalid choice is specified (for example: argument --test: invalid choice: 'choice4' (choose from 'choice1', 'choice2', 'choice3')). The trade-off is that CLI changes are required in order to take advantage of new choices.

Implementation

An example parser declaration:

choice_option.add_argument(
    '--test',
    metavar='<test>',
    choices=['choice1', 'choice2', 'choice3'],
    help=_('Test type (choice1, choice2 or choice3)'),
)

Options with Multiple Values

Some options can be repeated to build a collection of values for a property. Adding a value to the collection must be provided via the set action. Removing a value from the collection must be provided via an unset action. As a convenience, removing all values from the collection may be provided via a --no option on the set action and a --all option on unset action. If both --no option and option are specified, the values specified on the command would overwrite the collection property instead of appending on the set action. The --all option must be part of a mutually exclusive group with the related property option on the unset action, overwrite case don't exist in unset action.

An example behavior for set action:

Append:

object set --example-property xxx

Overwrite:

object set --no-example-property --example-property xxx

The example below assumes a property that contains a list of unique values. However, this example can also be applied to other collections using the appropriate parser action and action implementation (e.g. a dict of key/value pairs). Implementations will vary depending on how the REST API handles adding/removing values to/from the collection and whether or not duplicate values are allowed.

Implementation

An example parser declaration for set action:

parser.add_argument(
    '--example-property',
    metavar='<example-property>',
    dest='example_property',
    action='append',
    help=_('Example property for this <resource> '
           '(repeat option to set multiple properties)'),
)
parser.add_argument(
    '--no-example-property',
    dest='no_example_property',
    action='store_true',
    help=_('Remove all example properties for this <resource> '
           '(specify both --example-property and --no-example-property'
           ' to overwrite the current example properties)'),
)

An example handler in take_action() for set action:

if parsed_args.example_property and parsed_args.no_example_property:
    kwargs['example_property'] = parsed_args.example_property
elif parsed_args.example_property:
    kwargs['example_property'] = \
        resource_example_property + parsed_args.example_property
elif parsed_args.no_example_property:
    kwargs['example_property'] = []

An example parser declaration for unset action:

example_property_group = parser.add_mutually_exclusive_group()
example_property_group.add_argument(
    '--example-property',
    metavar='<example-property>',
    dest='example_property',
    action='append',
    help=_('Example property for this <resource> '
           '(repeat option to remove multiple properties)'),
)
example_property_group.add_argument(
    '--all-example-property',
    dest='all_example_property',
    action='store_true',
    help=_('Remove all example properties for this <resource>'),
)

An example handler in take_action() for unset action:

if parsed_args.example_property:
    kwargs['example_property'] = \
        list(set(resource_example_property) - \
             set(parsed_args.example_property))
if parsed_args.all_example_property:
    kwargs['example_property'] = []

Required Options

Some options have no default value and the API does not allow them to be None, then these options are always required when users use the command to which these options belong.

Required options must be validated by the CLI to avoid omissions. The CLI validation may provide an error message for the user if a required option is not specified. (for example: error: argument --test is required)

--test

Test option (required)

Implementation

The parser declaration should look like this:

parser.add_argument(
    '--test',
    metavar='<test>',
    required=True,
    help=_('Test option (required)'),
)

List Command Options

Additional Fields

Most list commands only return a subset of the available fields by default. Additional fields are available with the --long option. All list commands should allow --long even if they return all fields by default.

--long

List additional fields in output

Implementation

The parser declaration should look like this:

parser.add_argument(
    '--long',
    action='store_true',
    default=False,
    help='List additional fields in output',
)

Pagination

There are many ways to do pagination, some OpenStack APIs support it, some don't. OpenStackClient attempts to define a single common way to specify pagination on the command line.

--marker <marker>

Anchor for paging

--limit <limit>

Limit number of <resource> returned (integer)

Implementation

The parser declaration should look like this:

parser.add_argument(
    "--marker",
    metavar="<marker>",
    help="Anchor for paging",
)

parser.add_argument(
    "--limit",
    metavar="<limit>",
    type=int,
    help="Limit the number of <resource> returned",
)