Click

Personally more prefer Click than argparse.

Install Click with:

pip install click

or with python2 and python3 compatible:

pip3 install click

For more details, please refer here

This page serves for simplified cheatsheet for quick reference.

Basic Examples

Basic

Click uses decorator on functions to achieve CLI function.

import click

@click.command()
def hello():
    click.echo('Hello World!')

if __name__ == '__main__':
    hello()

$ python hello.py
Hello World!

Arguments and Options

import click

@click.command()
@click.option('--count', default=1, help='number of greetings')
@click.option('--dummy-args', default=1, help='example of multi-options')
@click.argument('name')
def hello(count, name, dummy_args):
    for x in range(count):
        click.echo('Hello %s!' % name)

if __name__ == '__main__':
    hello()

$ python hello.py --help
Usage: hello.py [OPTIONS] NAME

Options:
  --count INTEGER  number of greetings
  --dummy-args  INTEGER  example of multi-options
  --help           Show this message and exit.

Detailed description

Arguments

Arguments are mandatory inputs, usually takes as 1 param or a list of params with same meaning.

@click.argument(param_decls=None, type=None, required=False, default=None, callback=None, nargs=None, metavar=None, expose_value=True, is_eager=False, envvar=None, autocompletion=None)

Field	Description
param_decls	Parameter declarations
type	the type that should be used. Either a Parameter Type or a Python type. The later is converted into the former automatically if supported.
required	controls if this is optional or not.
default	the default value if omitted. This can also be a callable, in which case it’s invoked when the default is needed without any arguments.
callback	a callback that should be executed after the parameter was matched. This is called as fn(ctx, param, value) and needs to return the value. Before Click 2.0, the signature was (ctx, value).
nargs	the number of arguments to match. If not 1 the return value is a tuple instead of single value. The default for nargs is 1 (except if the type is a tuple, then it’s the arity of the tuple).
metavar	how the value is represented in the help page.
expose_value	if this is True then the value is passed onwards to the command callback and stored on the context, otherwise it’s skipped.
is_eager	eager values are processed before non eager ones. This should not be set for arguments or it will inverse the order of processing.
envvar	a string or list of strings that are environment variables that should be checked.

Options

Options are inputs that with name declared. Usually they are optional, with default value instead if not assigned in command.

Fields in Arguments is also supported.

@click.option(param_decls=None, show_default=False, prompt=False, confirmation_prompt=False, hide_input=False, is_flag=None, flag_value=None, multiple=False, count=False, allow_from_autoenv=True, type=None, help=None, hidden=False, show_choices=True, show_envvar=False, **attrs)

Field	Description
param_decls	Parameter declarations
show_default	controls if the default value should be shown on the help page.
show_envvar	controls if an environment variable should be shown on the help page.
prompt	if set to True or a non empty string then the user will be prompted for input. If set to True the prompt will be the option name capitalized.
confirmation_prompt	if set then the value will need to be confirmed if it was prompted for.
hide_input	if this is True then the input on the prompt will be hidden from the user. This is useful for password input.
is_flag	forces this option to act as a flag. The default is auto detection.
flag_value	which value should be used for this flag if it’s enabled. This is set to a boolean automatically if the option string contains a slash to mark two options.
multiple	if this is set to True then the argument is accepted multiple times and recorded. This is similar to nargs in how it works but supports arbitrary number of arguments.
count	this flag makes an option increment an integer.
allow_from_autoenv	if this is enabled then the value of this parameter will be pulled from an environment variable in case a prefix is defined on the context.
help	the help string.
hidden	hide this option from help outputs.

Terms Detailed Description

Parameter Declarations

Examples:

• For an option with ('-f', '--foo-bar'), the parameter name is foo_bar.

• For an option with ('-x',), the parameter is x.

• For an option with ('-f', '--filename', 'dest'), the parameter name is dest.

• For an option with ('--CamelCaseOption',), the parameter is camelcaseoption.

• For an arguments with (`foogle`), the parameter name is foogle.

Parameter Types

Type	Description
click.STRING	Unicode strings
click.INT	Integers
click.FLOAT	Floating point values
click.BOOL	Boolean values 1, yes, y, t, true => True 0, no, n, f, false => False
click.UUID	UUID values
click.File(mode='r', encoding=None, errors='strict', lazy=None, atomic=False)	Auto-load path input and return as file object. Auto-close when the context tear down.
click.Path(exists=False, file_okay=True, dir_okay=True, writable=False, readable=True, resolve_path=False, allow_dash=False, path_type=None)	Path which may not be exist resolve_path - The path will be parssed as absolute path, except tilde(~)
click.Choice(choices, case_sensitive=True)	Value only can be within list of choices
click.IntRange(min=None, max=None, clamp=False)	Integer Range. clamp - the values will be capped if value input exceeds the range
click.FloatRange(min=None, max=None, clamp=False)	Floating point Range
click.DateTime(formats=None)	Load date strings and parse into datetime formats – A list or tuple of date format strings, in the order in which they should be tried. Defaults to %Y-%m-%d, %Y-%m-%dT%H:%M:%S, %Y-%m-%d %H:%M:%S.