Argument (Tab) Completion Support

MILC supports argument completion out of the box using argcomplete. Getting argument completion to actually work can be a little fiddly, this page attempts to help you with that.

Prerequisites

Before argument completion will work your program must be registered with your shell. The most compatible way to do so is this:

eval "$(register-python-argcomplete my-program)"

If you have a new enough shell (EG bash 4.2 or later, zsh, fish) you can instead rely on activate-global-python-argcomplete, but in my experience that mechanism is fragile and easily broken.

Using Tab Completion

After running the command above you should be able to type the name of your program, type a partial flag name, and tab complete the rest. For many simple programs this is all you need.

Adding Custom Completions

In some cases you need to give argcomplete a custom list of completions. For example, if you want to complete hostnames out of a configuration file. You can specify this by setting completer in your argument decorator. You can use either callable or readline-style completers when you specify that.

For example, to use an EnvironCompleter for an argument:

def EnvironCompleter(**kwargs):
    return os.environ

@cli.argument('-e', '--env', completer=EnvironCompleter, help='Environment Variable')
@cli.entrypoint('My cool program')
def my_program(cli):
    pass