Not support upper case option.

import click
@click.command()
@click.option('-act', default='start')
@click.option('-D', default=False)
def inout(D, act):
    print(D, act)

inout()

This code not work: Error: no such option: -d

[ThiefMaster]

Since Python variables should be snake_case it makes sense for click to convert them to lowercase. You can override the name of the kwarg if you prefer something different.

[ThiefMaster]

Generally, short (single-letter) options use a single dash, while long options use two dashes. Almost all command line tools do this.

Actually looking at your error again, you define -d but your option is named -D. Keep in mind that options are case sensitive!