CLI

An extremely easy to use library to generate python CLIs from functions through introspection.

Available on pip: pip install cmcaine-cli

Automatically generate the equivalent of this:

import argparse
parser = argparse.ArgumentParser(description="Generate a cryptographic token with a given entropy.")
parser.add_argument('method', nargs='?', default='xkcd', choices=('xkcd', 'short'))
parser.add_argument('entropy', nargs='?', default=70, type=int)
args = parser.parse_args()

if args.method == 'xkcd':
    print(xkcd(args.entropy))
else:
    print(alphanumeric(args.entropy))

from this:

from cli import Choice, cli

def token(method:Choice('xkcd', 'short')='xkcd', entropy=70):
    "Generate a cryptographic token with a given entropy."
    if method == 'xkcd':
	return xkcd(entropy)
    else:
	return alphanumeric(entropy)

cli(token)()

Explicitly, cli(token) creates a new function that accepts an array of strings, parses and automatically converts them according to rules derived from the function signature, applies the parsed arguments to the original token and prints the output. cli(token)() calls that function using the default sys.argv.

But wait, there's more!

Keyword arguments (optional or mandatory) are supported as is one varargs argument per function. Arguments will be automatically converted into the type of their default argument (if it is not None) or their type annotation.

The exact mapping from function signature to argparse rules is specified in the docstring of generate_parser(), but the idea is that it should be fairly intuitive.

You can even generate CLIs for a whole module (or any other object with function attributes):

import example
from cli import cli, opportunistic, coerce_number

# You can use opportunistic(coerce_number) to convert any string that looks
# like a number to a number so you don't have to annotate all the functions in a
# module. YMMV.
cli(example, default_type=opportunistic(coerce_number))()

# If you want one, you can get a reference to the current module with
# sys.modules[__name__]

Lower level API

generate_parser(your_function_here) will return an argparse.Parser instance. apply_namespace(your_function_here, namespace) will apply a namespace object (as returned by parser.parse_args()) to a function.

generate_parser_obj(your_module_or_class_here) will return an argparse.Parser with one subparser per callable on the

Code quality

The code is very short, clearly documented inline and all advertised features are tested.

Reference

Function signature interpretation:

• (POSITIONAL_ONLY, POSITIONAL_OR_KEYWORD) = positional
• positional with default = optional positional
• KEYWORD_ONLY = options
• defaults = defaults
  • Boolean special casing
    • If the default is True or False, the option does not take any arguments. Instead, if the option is given on the commandline, the opposite value to the default is given to the function.
  • Example:

def rm(*, force=False):
    pass

cli(rm)(['--force']) # ~== rm(force=True)
cli(rm)([]) # ~== rm(force=False)

• type annotations = type
  • If the type is callable, it is called by argparse on the relevant substring
  • If the type is bool, then coerce_bool will be called on the string given for that argument
  • Provide your own custom function or handle the strings in your function body if you need something fancier.

Special types:

• cli.Choice
  • def foo(x:Choice(1,2)) interpreted as add_argument('x', choices=(1,2), type=int)

Example function signatures that cli understands:

def example(positional, arguments):
    pass

def defaults(normally_one=1):
    pass

def typed(positional:bool, positional2:int):
    pass

# `keyword some-positional-arg --keyword2=foo --keyword1=4`
# turns into keyword("some-positional-arg", keyword1=4, keyword2="foo")
def keyword(positional, *, keyword1=3, keyword2='default_filename'):
    pass

# Mandatory keywords are bad, but you can have them if you want.
def mandatory_keywords(positional, *, keyword1, keyword2):
    pass

def varargs(pos1, pos2, *rest):
    pass

def choice_from_list(person:Choice('Ann', 'Bob', 'Charlie'))
    pass

# `flags --flag` is similar to flags(flag=True)
# `flags --inverse_flag` is similar to flags(inverse_flag=False)
def flags(*, flag=False, inverse_flag=True):
    pass

Related work

Other nice ways to make CLIs:

• docopt
• cli2