captain 6.1.0

Python cli scripts for humans

Captain

Easy python CLI scripts for people that just want get things done.

Usage

A valid captain CLI script needs just two things:

1. A Default class that extends captain.Command and has a handle() method (can be async):

   from captain import Command
   
   class Default(Command):
       async def handle(self, foo, bar):
           return 0
   

2. Calling captain.application() at the end of your script:

   from captain import Command, application
   
   class Default(Command):
       async def handle(self, foo, bar):
           return 0
   
   if __name__ == "__main__":
       application()
   

That's it! Whatever arguments you define in your class's Default.handle() method will be options on the command line. A captain script is called just like any other python command line script, so to run the above example you could do:

$ python path/to/script.py --foo=1 --bar=2

Argument Decorator

The captain.arg() decorator provides a nice passthrough api to the full argparse.ArgumentParser.add_argument() method if you want to fine tune how arguments are passed into your script:

from captain import Command, application, arg

class Default(Command):
    @arg('--foo', '-f', action="store_true")
    @arg('arg', metavar='ARG')
    async def handle(self, *args, **kwargs):
        '''this is the help description'''
        self.output.out(args)
        self.output.out(kwargs)

if __name__ == "__main__":
    application()

Would print a help string like this:

usage: script.py [-h] [--foo FOO] ARG

this is the help description

positional arguments:
  ARG

optional arguments:
  -h, --help         show this help message and exit
  --foo FOO, -f FOO

Command Output

The captain.io.Output class makes it easy to print stuff in your script while still giving you full control by being able to configure the logger if you need to. It also will obey the global --quiet flag that Captain adds to every script.

It's available in the handle() method by using self.output:

from captain import Command

class Default(Command):
    async def handle(self, *args, **kwargs):
        var1 = "print"

        var2 = "stdout"
        self.output.out("this will {} to {}", var1, var2)

        var2 = "stderr"
        self.output.err("this will {} to {}", var1, var2)

        e = ValueError("this will print with stacktrace and everything")
        self.output.exception(e)

The captain.io.Output class has a lot of nice little helper methods but Captain can also work with modules like clint if you need to do more advanced cli output.

Examples

A typical python cli script

import argparse

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='fancy script description')
    parser.add_argument("--foo", action='store_true')
    parser.add_argument("--bar", default=0, type=int)
    parser.add_argument("args", nargs='*')
    args = parser.parse_args()
    sys.exit(0)

would become:

import captain

class Default(captain.Command):
    async def handle(self, *args, foo: bool = False, bar:int = 0):
        """fancy script description"""
        return 0

if __name__ == '__main__':
    captain.application()

Subcommands

Captain supports multiple subcommands defined in the script by naming your captain.Command child classes something other than Default:

# cli.py

import captain

class Foo(captain.Command):
    async def handle(self):
        self.output.out("Foo called")

class Bar(captain.Command):
    async def handle(self):
        self.output.out("Bar called")

if __name__ == '__main__':
    captain.application()

So foo could be called using:

$ python cli.py foo
Foo called

And bar could be called using:

$ python cli.py bar
Bar called

Embedding captain in another package

If you want a script from you package to be usable using both python -m example and maybe a console_scripts entry point defined in setup.py, you can set up your package's __main__.py module like this:

# example/__main__.py

from captain import Command, application

class Default(captain.Command):
    async def handle(self):
        pass
        
if __name__ == "__main__":
    application()

And then in your setup.py script you can add:

entry_points = {
    'console_scripts': [
        'example = example.__main__:application'
    ],
}

That's all there is to it.

Install

Use pip:

$ pip install captain

For latest and greatest:

$ pip install -U "git+https://github.com/Jaymon/captain#egg=captain"