Typer: CLIs with autocompletion. While developing and using.

---

Documentation: https://typer.tiangolo.com

Source Code: https://github.com/tiangolo/typer

---

Typer is library to build CLI applications that users love using and developers love creating. Based on Python 3.6+ type hints.

Typer is the little sibling of FastAPI. And it's intended to be the FastAPI of CLIs.

The key features are:

• Intuitive to write: Great editor support. Completion everywhere. Less time debugging. Designed to be easy to use and learn. Less time reading docs.
• Easy to use: It's easy to use for the final users. Automatic help commands, and (optional) automatic completion for all shells.
• Short: Minimize code duplication. Multiple features from each parameter declaration. Fewer bugs.
• Start simple: The simplest example adds only 2 lines of code to your app: 1 import, 1 function call.
• Grow large: Grow in complexity as much as you want create arbitrarily complex trees of commands and groups sub-commands, with options and arguments.

Requirements

Python 3.6+

Typer stands on the shoulders of a giant. Internally it uses Click, that's the only dependency.

Installation

pip install typer

Example

The absolute minimum

• Create a file main.py with:

import typer


def main(name: str):
    typer.echo(f"Hello {name}")


if __name__ == "__main__":
    typer.run(main)

Run it

Run your application:

python main.py

you will get a response like:

Usage: main.py [OPTIONS] NAME
Try "main.py --help" for help.

Error: Missing argument "NAME".

Now pass the NAME argument:

python main.py Camila

You will get a response like:

Hello Camila

And you automatically get a --help command:

python main.py --help

shows:

Usage: main.py [OPTIONS] NAME

Options:
  --help  Show this message and exit.

Example upgrade

The previous example was the extreme in terms of simplicity.

Now let's see one a bit more complex.

An example with two sub-commands

Modify the file main.py.

Create a typer.Typer() app, and create two sub-commands with their parameters.

import typer

app = typer.Typer()


@app.command()
def hello(name: str):
    typer.echo(f"Hello {name}")


@app.command()
def goodbye(name: str, formal: bool = False):
    if formal:
        typer.echo(f"Goodbye Ms. {name}. Have a good day.")
    else:
        typer.echo(f"Bye {name}!")


if __name__ == "__main__":
    app()

And that will:

• Explicitly create a typer.Typer app.
  • The previous typer.run actually creates one implicitly for you.
• Add two sub-commands with @app.command().
• Execute the app() itself, as if it was a function (instead of typer.run).

Run the upgraded example

Get the main --help:

python main.py --help

shows:

Usage: main.py [OPTIONS] COMMAND [ARGS]...

Options:
  --help  Show this message and exit.

Commands:
  goodbye
  hello

You have 2 sub-commands (the 2 functions), goodbye and hello.

Now get the help for hello:

python main.py hello --help

shows:

Usage: main.py hello [OPTIONS] NAME

Options:
  --help  Show this message and exit.

And now get the help for goodbye:

python main.py goodbye --help

shows:

Usage: main.py goodbye [OPTIONS] NAME

Options:
  --formal / --no-formal
  --help                  Show this message and exit.

Notice how it automatically creates a --formal and --no-formal for your bool option.

---

And of course, if you use it, it does what you expect:

python main.py hello Camila

shows:

Hello Camila

Then:

python main.py goodbye Camila

shows:

Bye Camila!

And:

python main.py goodbye --formal Camila

shows:

Goodbye Ms. Camila. Have a good day.

Recap

In summary, you declare once the types of parameters (arguments and options) as function parameters.

You do that with standard modern Python types.

You don't have to learn a new syntax, the methods or classes of a specific library, etc.

Just standard Python 3.6+.

For example, for an int:

total: int

or for a bool flag:

force: bool

And similarly for files, paths, enums (choices), etc. And there are tools to create groups of sub-commands, add metadata, extra validation, etc.

You get: great editor support, including completion and type checks everywhere.

Your users get: automatic --help, (optional) autocompletion in their terminal (Bash, Zsh, Fish, PowerShell).

For a more complete example including more features, see the Tutorial - User Guide.

Optional Dependencies

Typer uses Click internally. That's the only dependency.

But you can install extras:

• colorama: and Click will automatically use it to make sure colors always work correctly, even in Windows.
  • Then you can use any tool you want to output colors in all the systems, including the integrated typer.style() and typer.secho() (provided by Click).
  • Or any other tool, e.g. wasabi, blessings.
• click-completion: and Typer will automatically configure it to provide completion for all the shells, including installation commands.

You can install typer with colorama and click-completion with pip3 install typer[all].

Other tools and plug-ins

Click has many plug-ins available that you can use. And there are many tools that help with command line applications that you can use as well, even if they are not related to Typer or Click.

For example:

• click-spinner: to show the user that you are loading data. A Click plug-in.
  • • There are several other Click plug-ins at click-contrib that you can explore.
• tabulate: to automatically display tabular data nicely. Independent of Click or typer.
• etc... you can re-use many of the great available tools for building CLIs.

License

This project is licensed under the terms of the MIT license.