Extending the catkin command

The catkin command is designed to be easily extendable using the setuptools entry_points interface without modifying the catkin_tools project, itself. Regardless of what package the entry_point is defined in, it will be defined in the setup.py of that package, and will take this form:

from setuptools import setup

        'catkin_tools.commands.catkin.verbs': [
            # Example from catkin_tools' setup.py:
            # 'list = catkin_tools.verbs.catkin_list:description',
            'my_verb = my_package.some.module:description',

This entry in the setup.py places a file in the PYTHONPATH when either the install or the develop verb is given to setup.py. This file relates the key (in this case my_verb) to a module and attribute (in this case my_package.some.module and description). Then the catkin command will use the pkg_resources modules to retrieve these mapping at run time. Any entry for the catkin_tools.commands.catkin.verbs group must point to a description attribute of a module, where the description attribute is a dict. The description dict should take this form (the description from the build verb for example):

description = dict(
    description="Builds a catkin workspace",

This dict defines all the information that the catkin command needs to provide and execute your verb. The verb key takes a string which is the verb name (as shown in help and used for invoking the verb). The description key takes a string which is the description which is shown in the catkin -h output. The main key takes a callable (function) which is called when the verb is invoked. The signature of the main callable should be like this:

def main(opts):
    # ...
    return 0

Where the opts parameter is the Namespace object returns from ArgumentParser.parse_args(...) and should return an exit code which is passed to sys.exit.

The prepare_arguments key takes a function with this signature:

def prepare_arguments(parser):
    add = parser.add_argument
    # What packages to build
    add('packages', nargs='*',
        help='Workspace packages to build, package dependencies are built as well unless --no-deps is used. '
             'If no packages are given, then all the packages are built.')
    add('--no-deps', action='store_true', default=False,
        help='Only build specified packages, not their dependencies.')

    return parser

The above example is a snippet from the build verb’s prepare_arguments function. The purpose of this function is to take a given ArgumentParser object, which was created by the catkin command, and add this verb’s argparse arguments to it and then return it.

Finally, the argument_preprocessor command is an optional entry in the description dict which has this signature:

def argument_preprocessor(args):
    """Processes the arguments for the build verb, before being passed to argparse"""
    # CMake/make pass-through flags collect dashed options. They require special
    # handling or argparse will complain about unrecognized options.
    args = sys.argv[1:] if args is None else args
    extract_make_args = extract_cmake_and_make_and_catkin_make_arguments
    args, cmake_args, make_args, catkin_make_args = extract_make_args(args)
    # Extract make jobs flags.
    jobs_flags = extract_jobs_flags(' '.join(args))
    if jobs_flags:
        args = re.sub(jobs_flags, '', ' '.join(args)).split()
        jobs_flags = jobs_flags.split()
    extras = {
        'cmake_args': cmake_args,
        'make_args': make_args + (jobs_flags or []),
        'catkin_make_args': catkin_make_args,
    return args, extras

The above example is the argument_preprocessor function for the build verb. The purpose of the argument_preprocessor callable is to allow the verb to preprocess its own arguments before they are passed to argparse. In the case of the build verb, it is extracting the CMake and Make arguments before having them passed to argparse. The input parameter to this function is the list of arguments which come after the verb, and this function is only called when this verb has been detected as the first positional argument to the catkin command. So, you do not need to worry about making sure the arguments you just got are yours. This function should return a tuple where the first item in the tuple is the potentially modified list of arguments, and the second item is a dictionary of keys and values which should be added as attributes to the opts parameter which is later passed to the main callable. In this way you can take the arguments for your verb, parse them, remove some, add some or whatever, then you can additionally return extra information which needs to get passed around the argparse parse_args function. Most verbs should not need to do this, and in fact the built-in list verb’s description dict does not include one:

description = dict(
    description="Lists catkin packages in a given folder",

Hopefully, this information will help you get started when you want to extend the catkin command with custom verbs.