Tutorial

A Simple Example

Let’s start with a simple example. Just use optgroup for declaring option groups by decorating your command function in Click-like API style.

# app.py

import click
from click_option_group import optgroup, RequiredMutuallyExclusiveOptionGroup

@click.command()
@optgroup.group('Server configuration',
                help='The configuration of some server connection')
@optgroup.option('-h', '--host', default='localhost', help='Server host name')
@optgroup.option('-p', '--port', type=int, default=8888, help='Server port')
@optgroup.option('-n', '--attempts', type=int, default=3, help='The number of connection attempts')
@optgroup.option('-t', '--timeout', type=int, default=30, help='The server response timeout')
@optgroup.group('Input data sources', cls=RequiredMutuallyExclusiveOptionGroup,
                help='The sources of the input data')
@optgroup.option('--tsv-file', type=click.File(), help='CSV/TSV input data file')
@optgroup.option('--json-file', type=click.File(), help='JSON input data file')
@click.option('--debug/--no-debug', default=False, help='Debug flag')
def cli(**params):
    print(params)

if __name__ == '__main__':
    cli()

Now we can see help for our app:

$ python app.py --help
Usage: app.py [OPTIONS]

Options:
  Server configuration:           The configuration of some server connection
    -h, --host TEXT               Server host name
    -p, --port INTEGER            Server port
    -n, --attempts INTEGER        The number of connection attempts
    -t, --timeout INTEGER         The server response timeout
  Input data sources: [mutually_exclusive, required]
                                  The sources of the input data
    --tsv-file FILENAME           CSV/TSV input data file
    --json-file FILENAME          JSON input data file
  --debug / --no-debug            Debug flag
  --help                          Show this message and exit.

How It Works

Firstly, we declare the group using optgroup.group() decorator:

@optgroup.group('Server configuration', help='The configuration of some server connection')

Note

Also we can declare groups just using optgroup():

@optgroup('Server configuration', help='The configuration of some server connection')

Secondly, we declare the grouped options below using optgroup.option() decorator:

@optgroup.option('-h', '--host', default='localhost', help='Server host name')
@optgroup.option('-p', '--port', type=int, default=8888, help='Server port')

And that is all!

Checking Declarations

Attention

The important point: do not mix optgroup.option() and click.option() decorators!

click-option-group checks the decorators order and raises the exception if optgroup.option() and click.option() decorators are mixed.

The following code is incorrect:

@optgroup.group('My group')
@click.option('--hello')  # ERROR
@optgroup.option('--foo')
@click.option('--spam')  # ERROR
@optgroup.option('--bar')

The correct code looks like:

@click.option('--hello')
@optgroup.group('My group')
@optgroup.option('--foo')
@optgroup.option('--bar')
@click.option('--spam')

If we try to use optgroup.option without optgroup.grpup()/optgroup() declaration it also will raise the exception.

The following code is incorrect:

@click.command()
@click.option('--hello')
@optgroup.option('--foo')  # ERROR: Missing declaration of the option group
@optgroup.option('--bar')  # ERROR: Missing declaration of the option group
@click.option('--spam')
def cli(**params):
    pass

If we declare only option group without the options it will raise warning.

@click.command()
@click.option('--hello')
@optgroup.group('My group')  # WARN: The empty option group
@click.option('--spam')
def cli(**params):
    pass

API Features

Besides optgroup based decorators the package offers another way to declare grouped options using OptionGroup based class objects directly. We can use the instances of these classes and use its OptionGroup.option() method as decorator for declaring and adding options to the group.

Here is an example how it looks:

import click
from click_option_group import OptionGroup, RequiredMutuallyExclusiveOptionGroup

server_config = OptionGroup('Server configuration', help='The configuration of some server connection')
input_sources = RequiredMutuallyExclusiveOptionGroup('Input data sources', help='The sources of the input data')

@click.command()
@server_config.option('-h', '--host', default='localhost', help='Server host name')
@server_config.option('-p', '--port', type=int, default=8888, help='Server port')
@input_sources.option('--tsv-file', type=click.File(), help='CSV/TSV input data file')
@input_sources.option('--json-file', type=click.File(), help='JSON input data file')
@click.option('--debug/--no-debug', default=False, help='Debug flag')
def cli(**params):
    print(params)

if __name__ == '__main__':
    cli()

In this case initially we create group objects and then we use OptionGroup.option() method for declaring options.

As well as in above example we cannot mix option and click.option decorators. The following code is incorrect and will raise the exception:

@server_config.option('-h', '--host', default='localhost', help='Server host name')
@click.option('--foo')  # ERROR
@server_config.option('-p', '--port', type=int, default=8888, help='Server port')
@input_sources.option('--tsv-file', type=click.File(), help='CSV/TSV input data file')
@click.option('--bar')  # ERROR
@input_sources.option('--json-file', type=click.File(), help='JSON input data file')

Behavior and Relationship among Options

The groups are useful to define the specific behavior and relationship among grouped options.

click-option-groups provides two main classes: OptionGroup and GroupedOption.

  • OptionGroup class is a new entity for Click that provides the abstraction for grouping options and manage it.

  • GroupedOption class is inherited from click.Option and provides the functionality for grouped options.

OptionGroup and GroupedOption classes contain the basic functionality for support option groups. Both these classes do not contain the specific behavior or relationship among grouped options.

The specific behavior can be implemented by using the inheritance, mainly, in OptionGroup sub classes. click-option-groups provides some useful OptionGroup based classes out of the box:

OptionGroup based class can be specified via cls argument in optgroup()/optgroup.group() decorator or can be used directly when the second API way is used.

If you want to implement some complex behavior you can create a sub class of GroupedOption class and use your GroupedOption based class via cls argument in optgroup.option/OptionGroup.option decorator method:

@click.command()
@optgroup('My group', cls=MyCustomOptionGroup)
@optgroup.option('--foo', cls=MyCustomGroupedOption)
...

Limitations

The package does not support nested option groups (option subgroups). This is intentional. Nested option groups complicate the implementation, API and CLI and most often it is not necessary.

If you think you need to nested option groups try redesign your CLI and doing it with nesting commands.