Using Click

Warning

This is a more advanced topic, if you are starting with Typer, feel free to skip it.

It will be mostly useful for people that already work with Click and have questions around it.

Typer is powered by Click. It does all the work underneath.

Here is some more information related to using both together.

A single app with both Click and Typer

If you already have a Click application and want to migrate to Typer, or to add some Typer components, you can get a Click Command from your Typer application and then use Click directly.

How Click works

Before knowing how to combine Click and Typer, let's first check a little about how Click works.

Click Command

Any Click application has an object of class Command. That's, more or less, the most basic Click object.

A Command can have its own CLI arguments and CLI options, and it has a function that it calls.

For example, in this Click app:

import click


@click.command()
@click.option("--count", default=1, help="Number of greetings.")
@click.option("--name", prompt="Your name", help="The person to greet.")
def hello(count, name):
    """Simple program that greets NAME for a total of COUNT times."""
    for x in range(count):
        click.echo("Hello %s!" % name)


if __name__ == "__main__":
    hello()

The original hello variable is converted by Click from a function to a Command object. And the original hello function is used by that Command internally, but it is no longer named hello (as hello is now a Click Command).

Click Group

Then Click also has a Group class, it inherits from Command. So, a Group object is also a Command.

A Group can also have its own CLI arguments and CLI options.

A Group can have subcommands of class Command or sub groups of class Group as well.

And a Group can also have a function that it calls, right before calling the function for any specific subcommand.

For example:

import click


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


@click.command()
def initdb():
    click.echo("Initialized the database")


@click.command()
def dropdb():
    click.echo("Dropped the database")


cli.add_command(initdb)
cli.add_command(dropdb)


if __name__ == "__main__":
    cli()

The cli variable is converted by Click from a function to a Group object. And the original cli function is used by that Group internally.

Tip

The original cli function would be the equivalent of a Typer Callback.

Then the cli variable, that now is a Group object, is used to add sub-commands.

How Typer works

Typer doesn't modify the functions. You create an explicit variable of class typer.Typer and use it to register those functions.

And then, when you call the app, Typer goes and creates a Click Command (or Group), and then calls it.

If your app only has one command, then when you call it, Typer creates a single Click Command object and calls it.

But Typer creates a Click Group object if your app has any of:

• More than one command.
• A callback.
• Sub-Typer apps (sub commands).

Tip

If you want to learn more about this check the section One or Multiple Commands.

Combine Click and Typer

Typer uses an internal function typer.main.get_command() to generate a Click Command (or Group) from a typer.Typer object.

You can use it directly, and use the Click object with other Click applications.

Including a Click app in a Typer app

For example, you could have a Typer app, generate a Click Group from it, and then include other Click apps in it:

import click

import typer_cloup as typer

app = typer.Typer()


@app.command()
def top():
    """
    Top level command, form Typer
    """
    typer.echo("The Typer app is at the top level")


@app.callback()
def callback():
    """
    Typer app, including Click subapp
    """


@click.command()
@click.option("--name", prompt="Your name", help="The person to greet.")
def hello(name):
    """Simple program that greets NAME for a total of COUNT times."""
    click.echo("Hello %s!" % name)


typer_click_object = typer.main.get_command(app)

typer_click_object.add_command(hello, "hello")

if __name__ == "__main__":
    typer_click_object()

Notice that we add a callback that does nothing (only document the CLI program), to make sure Typer creates a Click Group. That way we can add sub-commands to that Click Group.

Then we generate a Click object from our typer.Typer app (typer_click_object), and then we can include another Click object (hello) in this Click Group.

And that way, our Typer app will have a subcommand top built with Typer, and a subcommand hello built with Click.

Check it:

$ python main.py

// Notice we have both subcommands, top and hello
Usage: main.py [OPTIONS] COMMAND [ARGS]...

Error: Missing command.

// Call the Typer part
$ python main.py top

The Typer app is at the top level

// Call the Click part
$ python main.py hello --name Camila

Hello Camila!

Including a Typer app in a Click app

The same way, you can do the contrary and include a Typer sub app in a bigger Click app:

import click

import typer_cloup as typer


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


@cli.command()
def initdb():
    click.echo("Initialized the database")


@cli.command()
def dropdb():
    click.echo("Dropped the database")


app = typer.Typer()


@app.command()
def sub():
    """
    A single-command Typer sub app
    """
    typer.echo("Typer is now below Click, the Click app is the top level")


typer_click_object = typer.main.get_command(app)

cli.add_command(typer_click_object, "sub")

if __name__ == "__main__":
    cli()

Notice that we don't have to add a callback or more commands, we can just create a Typer app that generates a single Click Command, as we don't need to include anything under the Typer app.

Then we generate a Click object from our typer.Typer app (typer_click_object), and then we use the Click cli to include our Click object from our Typer app.

In this case, the original Click app includes the Typer app.

And then we call the original Click app, not the Typer app.

Check it:

$ python main.py

// We get our Typer app down there in the sub command
Usage: main.py [OPTIONS] COMMAND [ARGS]...

Options:
  --help  Show this message and exit.

Commands:
  dropdb
  initdb
  sub     A single-command Typer sub app


// Use the Click part
$ python main.py initdb

Initialized the database

// And use the Typer part
$ python main.py sub

Typer is now below Click, the Click app is the top level

About Click decorators

Typer apps don't work with Click decorators directly.

This is because Typer doesn't modify functions to add metadata or to convert them to another object like Click does.

So, things like @click.pass_context won't work.

Most of the functionality provided by decorators in Click has an alternative way of doing it in Typer.

For example, to access the context, you can just declare a function parameter of type typer.Context.

Tip

You can read more about using the context in the docs: Commands: Using the Context

But if you need to use something based on Click decorators, you can always generate a Click object using the methods described above, and use it as you would normally use Click.