Typer
Typer, build great CLIs. Easy to code. Based on Python type hints.
Install / Use
/learn @fastapi/TyperREADME
Documentation: <a href="https://typer.tiangolo.com" target="_blank">https://typer.tiangolo.com</a>
Source Code: <a href="https://github.com/fastapi/typer" target="_blank">https://github.com/fastapi/typer</a>
Typer is a library for building <abbr title="command line interface, programs executed from a terminal">CLI</abbr> applications that users will love using and developers will love creating. Based on Python type hints.
It's also a command line tool to run scripts, automatically converting them to CLI applications.
The key features are:
- Intuitive to write: Great editor support. <abbr title="also known as auto-complete, autocompletion, IntelliSense">Completion</abbr> 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, and 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 of subcommands, with options and arguments.
- Run scripts: Typer includes a
typercommand/program that you can use to run scripts, automatically converting them to CLIs, even if they don't use Typer internally.
FastAPI of CLIs
Typer is <a href="https://fastapi.tiangolo.com" class="external-link" target="_blank">FastAPI</a>'s little sibling, it's the FastAPI of CLIs.
Installation
Create and activate a <a href="https://typer.tiangolo.com/virtual-environments/" class="external-link" target="_blank">virtual environment</a> and then install Typer:
<div class="termy">$ pip install typer
---> 100%
Successfully installed typer rich shellingham
Example
The absolute minimum
- Create a file
main.pywith:
def main(name: str):
print(f"Hello {name}")
This script doesn't even use Typer internally. But you can use the typer command to run it as a CLI application.
Run it
Run your application with the typer command:
// Run your application
$ typer main.py run
// You get a nice error, you are missing NAME
Usage: typer [PATH_OR_MODULE] run [OPTIONS] NAME
Try 'typer [PATH_OR_MODULE] run --help' for help.
╭─ Error ───────────────────────────────────────────╮
│ Missing argument 'NAME'. │
╰───────────────────────────────────────────────────╯
// You get a --help for free
$ typer main.py run --help
Usage: typer [PATH_OR_MODULE] run [OPTIONS] NAME
Run the provided Typer app.
╭─ Arguments ───────────────────────────────────────╮
│ * name TEXT [default: None] [required] |
╰───────────────────────────────────────────────────╯
╭─ Options ─────────────────────────────────────────╮
│ --help Show this message and exit. │
╰───────────────────────────────────────────────────╯
// Now pass the NAME argument
$ typer main.py run Camila
Hello Camila
// It works! 🎉
This is the simplest use case, not even using Typer internally, but it can already be quite useful for simple scripts.
Note: auto-completion works when you create a Python package and run it with --install-completion or when you use the typer command.
Use Typer in your code
Now let's start using Typer in your own code, update main.py with:
import typer
def main(name: str):
print(f"Hello {name}")
if __name__ == "__main__":
typer.run(main)
Now you could run it with Python directly:
<div class="termy">// Run your application
$ python main.py
// You get a nice error, you are missing NAME
Usage: main.py [OPTIONS] NAME
Try 'main.py --help' for help.
╭─ Error ───────────────────────────────────────────╮
│ Missing argument 'NAME'. │
╰───────────────────────────────────────────────────╯
// You get a --help for free
$ python main.py --help
Usage: main.py [OPTIONS] NAME
╭─ Arguments ───────────────────────────────────────╮
│ * name TEXT [default: None] [required] |
╰───────────────────────────────────────────────────╯
╭─ Options ─────────────────────────────────────────╮
│ --help Show this message and exit. │
╰───────────────────────────────────────────────────╯
// Now pass the NAME argument
$ python main.py Camila
Hello Camila
// It works! 🎉
Note: you can also call this same script with the typer command, but you don't need to.
Example upgrade
This was the simplest example possible.
Now let's see one a bit more complex.
An example with two subcommands
Modify the file main.py.
Create a typer.Typer() app, and create two subcommands with their parameters.
import typer
app = typer.Typer()
@app.command()
def hello(name: str):
print(f"Hello {name}")
@app.command()
def goodbye(name: str, formal: bool = False):
if formal:
print(f"Goodbye Ms. {name}. Have a good day.")
else:
print(f"Bye {name}!")
if __name__ == "__main__":
app()
And that will:
- Explicitly create a
typer.Typerapp.- The previous
typer.runactually creates one implicitly for you.
- The previous
- Add two subcommands with
@app.command(). - Execute the
app()itself, as if it was a function (instead oftyper.run).
Run the upgraded example
Check the new help:
<div class="termy">$ python main.py --help
Usage: main.py [OPTIONS] COMMAND [ARGS]...
╭─ Options ─────────────────────────────────────────╮
│ --install-completion Install completion │
│ for the current │
│ shell. │
│ --show-completion Show completion for │
│ the current shell, │
│ to copy it or │
│ customize the │
│ installation. │
│ --help Show this message │
│ and exit. │
╰───────────────────────────────────────────────────╯
╭─ Commands ────────────────────────────────────────╮
│ goodbye │
│ hello │
╰───────────────────────────────────────────────────╯
// When you create a package you get ✨ auto-completion ✨ for free, installed with --install-completion
// You have 2 subcommands (the 2 functions): goodbye and hello
Now check the help for the hello command:
$ python main.py hello --help
Usage: main.py hello [OPTIONS] NAME
╭─ Arguments ───────────────────────────────────────╮
│ * name TEXT [default: None] [required] │
╰───────────────────────────────────────────────────╯
╭─ Options ─────────────────────────────────────────╮
│ --help Show this message and exit. │
╰───────────────────────────────────────────────────╯
And now check the help for the goodbye command:
$ python main.py goodbye --help
Usage: main.py goodbye [OPTIONS] NAME
╭─ Arguments ───────────────────────────────────────╮
│ * name TEXT [default: None] [required] │
╰───────────────────────────────────────────────────╯
╭─ Options ─────────────────────────────────────────╮
│ --formal --no-formal [default: no-formal] │
│ --help Show this message │
│ and exit. │
╰───────────────────────────────────────────────────╯
// Automatic --formal and --no-formal for the bool option 🎉
Now you can try out the new command line application:
<div class="termy">// Use it with the hello command
$ python main.py hello Camila
Hello Camila
// And with the goodbye command
$ python main.py goodbye Camila
Bye Camila!
// And with --formal
$ python main.py goodbye --formal Camila
Goodbye Ms. Camila. Have a good day.
Note: If your app only has one command, by default the command name is omitted in usage: python main.py Camila. However, when there are multiple commands, you must explicitly include the command name: python main.py hello Camila. See One or Multiple Commands for more details.
Recap
In summary, you declare once the types of parameters (CLI arguments and CLI 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.
For exam
