This module provides functions and patterns for creating Command Line Interface (CLI) tools.
Commonly used, CLI related functions.
Extract a group of arguments from a list of arguments using a delimiter.
Here is an example:
>>> extract_argument_group(['foo', '--args', 'bar', '--baz'], '--args')
(['foo'], ['bar', '--baz'])
The group can always be ended using the double hyphen --. In order to pass a double hyphen as arguments, use three hyphens ---. Any set of hyphens encountered after the delimiter, and up to --, which have three or more hyphens and are isolated, will be captured and reduced by one hyphen.
For example:
>> extract_argument_group(['foo',
'--args', 'bar', '--baz', '---', '--',
'--foo-option'], '--args')
(['foo', '--foo-option'], ['bar', '--baz', '--'])
In the result the -- comes from the --- in the input. The --args and the corresponding -- are removed entirely.
The delimiter and -- terminator combination can also happen multiple times, in which case the bodies of arguments are combined and returned in the order they appeared.
For example:
>> extract_argument_group(['foo',
'--args', 'ping', '--',
'bar',
'--args', 'pong', '--',
'baz',
'--args', '--'], '--args')
(['foo', 'bar', 'baz'], ['ping', 'pong'])
Note: -- cannot be used as the delimiting_option.
| Parameters: |
|
|---|---|
| Returns: | tuple of arguments before and after the delimiter. |
| Return type: | tuple |
| Raises : | ValueError if the delimiting_option is --. |
Extracts make job flags from a list of other make flags, i.e. -j8 -l8
The input arguments are given as a string separated by whitespace. Make job flags are matched and removed from the arguments, and the Make job flags and what is left over from the input arguments are returned.
If no job flags are encountered, then an empty string is returned as the first element of the returned tuple.
Examples:
>> extract_jobs_flags('-j8 -l8')
('-j8 -l8', '')
>> extract_jobs_flags('-j8 ')
('-j8', ' ')
>> extract_jobs_flags('target -j8 -l8 --some-option')
('-j8 -l8', 'target --some-option')
>> extract_jobs_flags('target --some-option')
('', 'target --some-option')
| Parameters: | arguments (str) – string of space separated arguments which may or may not contain make job flags |
|---|---|
| Returns: | tuple of make jobs flags as a space separated string and leftover arguments as a space separated string |
| Return type: | tuple |
The verb pattern is a pattern where a single command aggregates multiple related commands by taking a required positional argument which is the “verb” for the action you want to perform. For example, catkin build is an example of a command and verb pair, where catkin is the command and build is the verb. In this example, the catkin command groups “actions” which are related to catkin together using verbs like build which will build a workspace of catkin packages.
This is an example boilerplate of a command which will use verbs:
from __future__ import print_function
import argparse
import sys
from osrf_pycommon.cli_utils.verb_pattern import create_subparsers
from osrf_pycommon.cli_utils.verb_pattern import list_verbs
from osrf_pycommon.cli_utils.verb_pattern import split_arguments_by_verb
COMMAND_NAME = '<INSERT COMMAND NAME HERE>'
VERBS_ENTRY_POINT = '{0}.verbs'.format(COMMAND_NAME)
def main(sysargs=None):
# Assign sysargs if not set
sysargs = sys.argv[1:] if sysargs is None else sysargs
# Create a top level parser
parser = argparse.ArgumentParser(
description="{0} command".format(COMMAND_NAME)
)
# Generate a list of verbs available
verbs = list_verbs(VERBS_ENTRY_POINT)
# Create the subparsers for each verb and collect the arg preprocessors
argument_preprocessors, verb_subparsers = create_subparsers(
parser,
COMMAND_NAME,
verbs,
VERBS_ENTRY_POINT,
sysargs,
)
# Determine the verb, splitting arguments into pre and post verb
verb, pre_verb_args, post_verb_args = split_arguments_by_verb(sysargs)
# Short circuit -h and --help
if '-h' in pre_verb_args or '--help' in pre_verb_args:
parser.print_help()
sys.exit(0)
# Error on no verb provided
if verb is None:
print(parser.format_usage())
sys.exit("Error: No verb provided.")
# Error on unknown verb provided
if verb not in verbs:
print(parser.format_usage())
sys.exit("Error: Unknown verb '{0}' provided.".format(verb))
# Short circuit -h and --help for verbs
if '-h' in post_verb_args or '--help' in post_verb_args:
verb_subparsers[verb].print_help()
sys.exit(0)
# First allow the verb's argument preprocessor to strip any args
# and return any "extra" information it wants as a dict
processed_post_verb_args, extras = \
argument_preprocessors[verb](post_verb_args)
# Then allow argparse to process the left over post-verb arguments along
# with the pre-verb arguments and the verb itself
args = parser.parse_args(pre_verb_args + [verb] + processed_post_verb_args)
# Extend the argparse result with the extras from the preprocessor
for key, value in extras.items():
setattr(args, key, value)
# Finally call the subparser's main function with the processed args
# and the extras which the preprocessor may have returned
sys.exit(args.main(args) or 0)
This function is mostly boilerplate in that it will likely not change much between commands of different types, but it would also be less transparent to have this function created for you. If you are using this boilerplate to implement your command, then you should be careful to update COMMAND_NAME to reflect your command’s name.
This line defines the entry_point group for your command’s verbs:
VERBS_ENTRY_POINT = '{0}.verbs'.format(COMMAND_NAME)
In the case that your command is called foo then this would become foo.verbs. This name is important because it is how verbs for this command can be provided by your Python package or others. For example, each verb for your command foo will need entry in the setup.py of its containing package, like this:
setup(
...
entry_points={
...
'foo.verbs': [
'bar = foo.verbs.bar:entry_point_data',
],
}
)
You can see here that you are defining bar to be a an entry_point of type foo.verbs which in turn points to a module and reference foo.verbs.bar and entry_point_data. At run time this verb pattern will let your command lookup all things defined as foo.verbs and load up the reference to which they point.
In order to add a verb to your command, a few things must happen.
First you must have an entry in the setup.py as described above. This allows the command to find the entry_point for your verb at run time. The entry_point for these verbs should point to a dictionary which describes the verb being added.
This is an example of an entry_point_data dictionary for a verb:
entry_point_data = dict(
verb='build',
description='Builds a workspace of packages',
# Called for execution, given parsed arguments object
main=main,
# Called first to setup argparse, given argparse parser
prepare_arguments=prepare_arguments,
# Called after prepare_arguments, but before argparse.parse_args
argument_preprocessor=argument_preprocessor,
)
As you can see this dictionary describes the verb and gives references to functions which allow the command to describe the verb, hook into argparse parameter creation for the verb, and to execute the verb. The verb, description, main, and prepare_arguments keys of the dictionary are required, but the argument_preprocessor key is optional.
Here is an invented example of main, prepare_arguments, and argument_preprocessor:
def prepare_arguments(parser):
parser.add_argument('--some-argument', action='store_true', default=False)
return parser
def argument_preprocessor(args):
extras = {}
if '-strange-argument' in args:
args.remove('-strange-argument')
extras['strange_argument'] = True
return args, extras
def main(options):
print('--some-argument:', options.some_argument)
print('-strange-argument:', options.strange_argument)
if options.strange_argument:
return 1
return 0
The above example is simply to illustrate the signature of these functions and how they might be used.
API for implementing commands and verbs which used the verb pattern.
Call a prepare_arguments function with the correct number of parameters.
The prepare_arguments function of a verb can either take one parameter, parser, or two parameters parser and args, where args are the current arguments being processed.
| Parameters: |
|
|---|---|
| Returns: | return value of function or the parser if the function returns None. |
| Return type: | argparse.ArgumentParser |
| Raises : | ValueError if a function with the wrong number of parameters is given |
Creates argparse subparsers for each verb which can be discovered.
Using the verbs parameter, the availble verbs are iterated through. For each verb a subparser is created for it using the parser parameter. The cmd_name is used to fill the title and description of the add_subparsers function call. The group parameter is used with each verb to load the verb’s description, prepare_arguments function, and the verb’s argument_preprocessors if available. Each verb’s prepare_arguments function is called, allowing them to add arguments. Finally a list of argument_preprocessors functions and verb subparsers are returned, one for each verb.
| Parameters: |
|
|---|---|
| Returns: | tuple of argument_preprocessors and verb subparsers |
| Return type: | tuple |
Return unmodifed args and an empty dict for extras
List verbs available for a given entry_point group.
| Parameters: | group (str) – entry_point group name for the verbs to list |
|---|---|
| Returns: | list of verb names for the given entry_point group |
| Return type: | list of str |
Load description of a verb in a given group by name.
| Parameters: |
|
|---|---|
| Returns: | verb description |
| Return type: | dict |
Split arguments by verb.
Given a list of arguments (list of strings), the verb, the pre verb arguments, and the post verb arugments are returned.
For example:
>>> args = ['--command-arg1', 'verb', '--verb-arg1', '--verb-arg2']
>>> split_arguments_by_verb(args)
('verb', ['--command-arg1'], ['--verb-arg1', '--verb-arg2'])
| Parameters: | arguments (list) – list of system arguments |
|---|---|
| Returns: | the verb (str), pre verb args (list), and post verb args (list) |
| Return type: | tuple |