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Simple Multi Command Line Parser

Project description

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SMCLIP is a simple framework for parsing multi command line arguments using python’s builtin ArgumentParser. With SMCLIP you are able to built git-like commands. Commands are created by inheriting from base Command classes and extending their callbacks.

Core features includes:

  • building trees of multi-level sub-commands
  • support for default sub-commands (e.g. git stash [save])
  • support for fallback sub-commands (when sub-command is not found; e.g. catching ID)
  • support for chained sub-commands
  • sub-command lazy loading

Differences with …

Why you should choose SMCLIP when [X] supports sub-commands?

ArgumentParser

https://docs.python.org/3/library/argparse.html#sub-commands

Python’s ArgumentParser support sub-commands by adding sub-parsers to the parent parser. The ArgumentParser with sub-commands considers that a CLI application is simple and does simple operations. A CLI application starts can get confusing to users (in help) when there are more and more sub-commands being added.

Subparsers of ArgumentParser should be constructed prior to calling the base parser. Subparsers don not support any routing based on the commands.

Click

http://click.pocoo.org/latest/

Click utilizes Python’s decorators to create sub-commands hierarchy. Using decorators makes the code more readable. On the other hand, extending Click is done by creating new decorators. Supporting new parsing techniques (default or fallback commands) and conditional callback triggering is not done simplistically.

Cement

http://builtoncement.com/

Cement is a framework intended for complex CLI applications. Cement comes with multiple set of utilities (logging, caching). Command line parsing is a one part of Cement framework. Cement support sub-commands by nesting controllers. Default and fallback commands and conditional callback triggering is done by extending core controllers.

Argument Examples

# Simple command
(1)$ app help
         *--*
           +---- sub-command of base application

# Two commands
(2)$ app task list
(3)$ app --debug task list --listopt
     *----+----* *--* *-----+------*
           \       \         \
            \       \         +------- list sub-command with option
             \       +---------------- task command
              +----------------------- application with its own option

# fallback command
(4)$ app task 1234 --viewopt
              *-----+------*
                     \
                      +------- fallback command catching ID

# chained commands
(5)$ app task 1234 change --state ASSIGNED assign person
                   *----------+----------* *-----+-----*
                              |                   \
                               \                   +------ chained command
                                \                          with positional
                                 \                         argument
                                  \
                                   +---------------------- chained command
                                                           with option

Callbacks

preprocess

preprocess is called after successful parsing of command’s arguments. Invocation is done even when a sub-command is being called. preprocess is not called when default command is in effect.

this_action

this_action is a main callback for actions in current command. This callback is called after preprocess and only when current command is final (no other sub-commands are being invoked). Exceptions are chained command, in which the this_action is invoked every time.

results_callback

(commands group only)

results_callback is called after a sub-command invocation is done. A return value from sub-command, returned by this_action callback, is passed as a positional argument. Results from chained commands are wrapped and passed in ChainedOutputResults class object.

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