Installation is done via pip:

pip install click-repl

In your click app:

import click
from click_repl import register_repl

@click.group()
def cli():
    pass

@cli.command()
def hello():
    click.echo("Hello world!")

register_repl(cli)
cli()

In the shell:

$ my_app repl
> hello
Hello world!
> ^C
$ echo hello | my_app repl
Hello world!

Features not shown:

• Tab-completion.
• The parent context is reused, which means ctx.obj persists between subcommands. If you're keeping caches on that object (like I do), using the app's repl instead of the shell is a huge performance win.
• ! - prefix executes shell commands.

You can use the internal :help command to explain usage.

For more flexibility over how your REPL works you can use the repl function directly instead of register_repl. For example, in your app:

import click
from click_repl import repl
from prompt_toolkit.history import FileHistory

@click.group()
def cli():
    pass

@cli.command()
def myrepl():
    prompt_kwargs = {
        'history': FileHistory('/etc/myrepl/myrepl-history'),
    }
    repl(click.get_current_context(), prompt_kwargs=prompt_kwargs)
    
cli()

And then your custom myrepl command will be available on your CLI, which will start a REPL which has its history stored in /etc/myrepl/myrepl-history and persist between sessions.

Any arguments that can be passed to the python-prompt-toolkit Prompt class can be passed in the prompt_kwargs argument and will be used when instantiating your Prompt.