main_dec

A small library for painless commandline argument parsing in python.

Install

> pip install main-dec

Quickstart

# my_cli.py

from typing import Tuple

from main_dec import main


@main
def run(required_str: str, optional_int=1, optional_tuple: Tuple[int, ...]=()):
    """
    A small example cli
    
    :param required_str: a required str
    :param optional_int: an optional int
    :param optional_tuple: an optional tuple
    """
    print('required_str', required_str)
    print('optional_int', optional_int)
    print('optional_tuple', optional_tuple)

> python -m my_cli -h
usage: my_cli [-h] [--optional-tuple OPTIONAL_TUPLE [OPTIONAL_TUPLE ...]] [--optional-int OPTIONAL_INT] required_str

A small example cli

positional arguments:
  required_str          a required str

optional arguments:
  -h, --help            show this help message and exit
  --optional-tuple OPTIONAL_TUPLE [OPTIONAL_TUPLE ...]
                        an optional tuple
  --optional-int OPTIONAL_INT
                        an optional int

> python -m my_cli arg --optional-int 2 --optional-tuple 1 2 3
required_str arg
optional_int 2
optional_tuple (1, 2, 3)

Required and optional arguments

Positional arguments to your function will be parsed as required arguments to your cli. Optional arguments to your function will be parsed as optional arguments.

# my_cli.py

from main_dec import main


@main
def run(required_arg: str, optional_arg=''):
    pass

> python -m my_cli -h
usage: my_cli [-h] [--optional-arg OPTIONAL_ARG] required_arg

positional arguments:
  required_arg

optional arguments:
  -h, --help            show this help message and exit
  --optional-arg

Flags

Optional bool arguments are parsed as flags, such that passing them on the commandline "flips" their truthiness.

# my_cli.py

from main_dec import main

@main
def run(positive_flag=False, negative_flag=True):
    print('positive_flag', positive_flag)
    print('negative_flag', negative_flag)

> python -m my_cli --postive-flag --negative-flag
positive_flag True
negative_flag False

Type conversions

PEP484 annotated arguments and arguments with default values will have their types converted before they are passed to your function.

# my_cli.py

from typing import Tuple 

from main_dec import main


@main
def run(required_float: float, optional_tuple: Tuple[float, ...] = ()):
    print('required_float', required_float)
    print('optional_tuple', optional_tuple)

> python -m my_cli 1 --optional-tuple 2 3 4
required_float 1.0
optional_tuple (2.0, 3.0, 4.0)

Currently supported types are str, bytes, int, float, list (including typing.List), tuple (including typing.Tuple) and Enum. str is the default type for arguments that are not annotated and do not have a default value.

Tuple arguments

Tuple arguments can either be parsed as varied length tuples, or fixed length tuples.

Fixed length tuples are arguments that are annotated without ... as a type variable, or arguments with default values with mixed types

# my_cli.py

from typing import Tuple

from main_dec import main


@main
def run(fixed_length_tuple1: Tuple[int, int], fixed_length_tuple2=(1, 'arg')):
    pass

> python -m my_cli -h
usage: my_cli [-h] [--fixed-length-tuple2 FIXED_LENGTH_TUPLE2 FIXED_LENGTH_TUPLE2] fixed_length_tuple1 fixed_length_tuple1

positional arguments:
  fixed_length_tuple1

optional arguments:
  -h, --help            show this help message and exit
  --fixed-length-tuple2 FIXED_LENGTH_TUPLE2 FIXED_LENGTH_TUPLE2

Varied length tuples are arguments that

• Are annotated with ... as a type variable (e.g Tuple[int, ...])
• Are annotated simply with Tuple or tuple
• Have a tuple as a default value with homogeneous types (e.g (1, 2))

Enum arguments

Arguments annotated withEnum, or with a default Enum type, can be used to enforce that an argument must have certain values.

# my_cli.py

from enum import Enum

from main_dec import main

class Choice(Enum):
    first = 1
    second = 2

@main
def run(argument_with_choices: Choice):
    print('argument_with_choices', argument_with_choices)

> python -b my_cli -h
usage: my_cli [-h] {first,second}

positional arguments:
  {first,second}

optional arguments:
  -h, --help      show this help message and exit
 
> python -m my_cli second
argument_with_choices Choice.second

This can be combined with generic types such as typing.Tuple and typing.List, as well as arguments with default arguments that are tuple or list types with Enum elements.

CLI Documentation

Doc strings in ReST or Google style are parsed and used to create usage and help messages

# my_cli.py

from main_dec import main

@main
def run(arg: str):
    """
    An example cli
    
    :param arg: A required argument
    """

> python -m my_cli -h
usage: my_cli [-h] arg

An example cli

positional arguments:
  arg         A required argument

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