Option groups

The @option_group decorator

The recommended way of defining option groups is through the decorator option_group().

cloup.option_group(name, *args, **kwargs)[source]

Returns a decorator that annotates a function with an option group.

The help is an optional description and can be provided either as keyword argument or as 2nd positional argument after the name of the group:

# help as keyword argument
@option_group(name, *options, help=None, ...)

# help as 2nd positional argument
@option_group(name, help, *options, ...)
Parameters

  • name – this is shown as heading of the help section describing the option group.

  • help – an optional description shown below the name; can be provided as keyword argument or 2nd positional argument.

  • options – an arbitrary number of decorators like click.option, which annotate the input function with one Option.

  • constraint – an optional instance of Constraint (see Constraints for more info); a description of the constraint will be shown between squared brackets aside the option group title (or below it if too long).

  • hidden – if True, the option group and all its options are hidden from the help page (all contained options will have their hidden attribute set to True).

import cloup
from cloup import option_group, option
from cloup.constraints import SetAtLeast

@cloup.command('clouptest')
@option_group(
    "Input options",
    "This is a very long description of the option group. I don't think this is "
    "needed very often; still, if you want to provide it, you can pass it as 2nd "
    "positional argument or as keyword argument 'help' after all options.",
    option('-o', '--one', help='1st input option'),
    option('--two', help='2nd input option'),
    option('--three', help='3rd input option'),
)
@option_group(
    'Output options',
    option('--four / --no-four', help='1st output option'),
    option('--five', help='2nd output option'),
    option('--six', help='3rd output option'),
    constraint=RequireAtLeast(1),
)
# Options that don't belong to any option group (including --help)
# are shown under "Other options"
@option('--seven', help='first uncategorized option',
        type=click.Choice(['yes', 'no', 'ask']))
@option('--height', help='second uncategorized option')
def cli(**kwargs):
    """ A CLI that does nothing. """
    print(kwargs)

Usage: clouptest [OPTIONS]

  A CLI that does nothing.

Input options:
  This is a very long description of the option group. I don't think this is
  needed very often; still, if you want to provide it, you can pass it as
  2nd positional argument or as keyword argument 'help' after all options.
  -o, --one TEXT        1st input option
  --two TEXT            2nd input option
  --three TEXT          3rd input option

Output options: [at least 1 required]
  --four / --no-four    1st output option
  --five TEXT           2nd output option
  --six TEXT            3rd output option

Other options:
  --seven [yes|no|ask]  first uncategorized option
  --height TEXT         second uncategorized option
  --help                Show this message and exit.

The default option group

Options that are not assigned to any user-defined option group are listed under a section which is shows at the bottom. This section is titled “Other options”, unless the default group is the only one defined, in which case cloup.Command behaves like a normal click.Command, naming it just “Options”.

In the example above, I used the cloup.option() decorator to define options but you can use click.option() as well. There’s no practical difference between the two when using @option_group.

Aligned vs non-aligned groups

By default, all option group help sections are aligned, meaning that they share the same column widths. Many people find this visually pleasing and this is also the default behavior of argparse.

Nonetheless, if some of your option groups have shorter options, alignment may result in a lot of wasted space and definitions quite far from option names, which is bad for readability. See this biased example to compare the two modes:

Usage: clouptest [OPTIONS]

  A CLI that does nothing.

Input options:
  --one TEXT                   This description is more likely to be wrapped
                               when aligning
  --two TEXT                   This description is more likely to be wrapped
                               when aligning
  --three TEXT                 This description is more likely to be wrapped
                               when aligning

Output options:
  --four                       This description is more likely to be wrapped
                               when aligning
  --five TEXT                  This description is more likely to be wrapped
                               when aligning
  --six TEXT                   This description is more likely to be wrapped
                               when aligning

Other options:
  --seven [a|b|c|d|e|f|g|h|i]  First uncategorized option
  --height TEXT                Second uncategorized option
  --help                       Show this message and exit.

Usage: clouptest [OPTIONS]

  A CLI that does nothing.

Input options:
  --one TEXT    This description is more likely to be wrapped when aligning.
  --two TEXT    This description is more likely to be wrapped when aligning.
  --three TEXT  This description is more likely to be wrapped when aligning.

Output options:
  --four       This description is more likely to be wrapped when aligning.
  --five TEXT  This description is more likely to be wrapped when aligning.
  --six TEXT   This description is more likely to be wrapped when aligning.

Other options:
  --seven [a|b|c|d|e|f|g|h|i]  First uncategorized option.
  --height TEXT                Second uncategorized option.
  --help                       Show this message and exit.

In Cloup, you can format each option group independently from each other setting the @command parameter align_option_groups=False. Since v0.8.0, this parameter is also available as a Context setting:

from cloup import Context, group

CONTEXT_SETTINGS = Context.settings(
    align_option_groups=False,
    ...
)

@group(context_settings=CONTEXT_SETTINGS)
def main():
    pass

Note

The problem of aligned groups can sometimes be solved decreasing the HelpFormatter parameter max_col1_width, which defaults to 30.

Alternative APIs

Option groups without nesting

While I largely prefer @option_group, you may not like the additional level of indentation it requires. In that case, you may prefer the following way of defining option groups:

from cloup import OptionGroup
from cloup.constraints import SetAtLeast

# OptionGroup takes all arguments of @option_group but *options
input_grp = OptionGroup(
    'Input options', help='This is a very useful description of the group')
output_grp = OptionGroup(
    'Output options', constraint=SetAtLeast(1))

@cloup.command('clouptest')
# Input options
@input_grp.option('-o', '--one', help='1st input option')
@input_grp.option('--two', help='2nd input option')
# Output options
@output_grp.option('--four / --no-four', help='1st output option')
@output_grp.option('--five', help='2nd output option')
def cli_flat(**kwargs):
    """ A CLI that does nothing. """
    print(kwargs)

Equivalently, you could pass the option group as an argument to cloup.option:

@cloup.option('-o', '--one', help='1st input option', group=input_grp)

Note that, in both cases, OptionGroup instances work as “markers” for options, not as containers of options: when you add an option nothing happens to the corresponding option group.

Option groups without decorators

For some reason, you may need to work at a lower level, by passing parameters to a Command constructor. In that case you can use GroupedOption:

from cloup import Command, GroupedOption, OptionGroup

output_opts = OptionGroup("Output options")

params = [
    GroupedOption('--verbose', is_flag=True, group=output_opts),
    ...
]

cmd = Command(..., params=params, ...)

Reusing/modularizing option groups

Some people have asked how to reuse option groups in multiple commands and how to put particularly long option groups in their own files. This is easy if you know how Python decorator works. First, you store the decorator returned by option_group (called without a @) in a variable:

from cloup import option_group

output_options = option_group(
    "Output options",
    option(...),
    option(...),
    ...
)

Then you can use the decorator as many times as you want:

@command()
# other decorators...
@output_options
# other decorators ...
def foo()
    ...

Of course, if output_options is defined in a different file, don’t forget to import it!

Terminology-nazi note

It’s worth noting that output_options in the example above is not an option group, it’s just a function that recreate the same OptionGroup object and all its options every time it is called. So, technically, you’re not “reusing an option group”.

How it works

This feature is implemented simply by annotating each option with an additional attribute group of type Optional[OptionGroup]. Unless the option is of class GroupedOption, this group attribute is added and set by monkey-patching.

When the command is initialized, OptionGroupMixin groups all options by their group attribute. Options that don’t have a group attribute or have it set to None are put into the “default option group” (together with --help).

In order to show option groups in the command help, OptionGroupMixin “overrides” Command.format_options.

Feature support

This features depends on two mixins:

cloup.Command is the only command class that supports this feature, including both these mixins.

Attention

cloup.Group doesn’t support option groups nor constraints. This is intentional: a Group should have only a few options, so they should not need neither option groups nor constraints. (But I may be wrong; if you disagree, open an issue describing your use case). Anyway, you can easily subclass cloup.Group to include the above mixins:

from cloup import ConstraintMixin, OptionGroupMixin, Group

class MyGroup(ConstraintMixin, OptionGroupMixin, Group):
    pass