Python Click - Supply arguments and options from a configuration file

Question

Given the following program:

#!/usr/bin/env python
import click

@click.command()
@click.argument("arg")
@click.option("--opt")
@click.option("--config_file", type=click.Path())
def main(arg, opt, config_file):
    print("arg: {}".format(arg))
    print("opt: {}".format(opt))
    print("config_file: {}".format(config_file))
    return

if __name__ == "__main__":
    main()

I can run it with the arguments and options provided through command line.

$ ./click_test.py my_arg --config_file my_config_file
arg: my_arg
opt: None
config_file: my_config_file

How do I provide a configuration file (in ini? yaml? py? json?) to --config_file and accept the content as the value for the arguments and options?

For instance, I want my_config_file to contain

opt: my_opt

and have the output of the program show:

$ ./click_test.py my_arg --config_file my_config_file
arg: my_arg
opt: my_opt
config_file: my_config_file

I've found the callback function which looked to be useful but I couldn't find a way to modify the sibling arguments/options to the same function.

Answer 1

This can be done by over riding the click.Command.invoke() method like:

Custom Class:

def CommandWithConfigFile(config_file_param_name):

    class CustomCommandClass(click.Command):

        def invoke(self, ctx):
            config_file = ctx.params[config_file_param_name]
            if config_file is not None:
                with open(config_file) as f:
                    config_data = yaml.safe_load(f)
                    for param, value in ctx.params.items():
                        if value is None and param in config_data:
                            ctx.params[param] = config_data[param]

            return super(CustomCommandClass, self).invoke(ctx)

    return CustomCommandClass

Using Custom Class:

Then to use the custom class, pass it as the cls argument to the command decorator like:

@click.command(cls=CommandWithConfigFile('config_file'))
@click.argument("arg")
@click.option("--opt")
@click.option("--config_file", type=click.Path())
def main(arg, opt, config_file):

Test Code:

# !/usr/bin/env python
import click
import yaml

@click.command(cls=CommandWithConfigFile('config_file'))
@click.argument("arg")
@click.option("--opt")
@click.option("--config_file", type=click.Path())
def main(arg, opt, config_file):
    print("arg: {}".format(arg))
    print("opt: {}".format(opt))
    print("config_file: {}".format(config_file))


main('my_arg --config_file config_file'.split())

Test Results:

arg: my_arg
opt: my_opt
config_file: config_file