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CLI Arguments with Help

In the First Steps section you saw how to add help for a CLI app/command by adding it to a function's docstring.

Here's how that last example looked like:

import typer


def main(name: str, lastname: str = "", formal: bool = False):
    """
    Say hi to NAME, optionally with a --lastname.

    If --formal is used, say hi very formally.
    """
    if formal:
        typer.echo(f"Good day Ms. {name} {lastname}.")
    else:
        typer.echo(f"Hello {name} {lastname}")


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

Now that you also know how to use typer.Argument(), let's use it to add documentation specific for a CLI argument.

Add a help text for a CLI argument

You can use the help parameter to add a help text for a CLI argument:

import typer


def main(name: str = typer.Argument(..., help="The name of the user to greet")):
    typer.echo(f"Hello {name}")


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

And it will be used in the automatic --help option:

$ python main.py --help

// Check the section with Arguments below 🚀
Usage: main.py [OPTIONS] NAME

Arguments:
  NAME  The name of the user to greet  [required]

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.

Combine help text and docstrings

And of course, you can also combine that help with the docstring:

import typer


def main(name: str = typer.Argument(..., help="The name of the user to greet")):
    """
    Say hi to NAME very gently, like Dirk.
    """
    typer.echo(f"Hello {name}")


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

And the --help option will combine all the information:

$ python main.py --help

// Notice that we have the help text from the docstring and also the Arguments 📝
Usage: main.py [OPTIONS] NAME

  Say hi to NAME very gently, like Dirk.

Arguments:
  NAME  The name of the user to greet  [required]

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.

Help with defaults

If you have a CLI argument with a default value, like "World":

import typer


def main(name: str = typer.Argument("World", help="Who to greet")):
    """
    Say hi to NAME very gently, like Dirk.
    """
    typer.echo(f"Hello {name}")


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

It will show that default value in the help text:

$ python main.py --help

// Notice the [default: World] 🔍
Usage: main.py [OPTIONS] [NAME]

  Say hi to NAME very gently, like Dirk.

Arguments:
  [NAME]  Who to greet  [default: World]

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.

But you can disable that if you want to, with show_default=False:

import typer


def main(name: str = typer.Argument("World", help="Who to greet", show_default=False)):
    """
    Say hi to NAME very gently, like Dirk.
    """
    typer.echo(f"Hello {name}")


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

And then it won't show the default value:

$ python main.py --help

// Notice the there's no [default: World] now 🔥
Usage: main.py [OPTIONS] [NAME]

  Say hi to NAME very gently, like Dirk.

Arguments:
  [NAME]  Who to greet

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.

Technical Details

In Click applications the default values are hidden by default. 🙈

In Typer these default values are shown by default. 👀

Custom default string

You can use the same show_default to pass a custom string (instead of a bool) to customize the default value to be shown in the help text:

import typer


def main(
    name: str = typer.Argument(
        "Wade Wilson", help="Who to greet", show_default="Deadpoolio the amazing's name"
    )
):
    typer.echo(f"Hello {name}")


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

And it will be used in the help text:

$ python main.py --help

Usage: main.py [OPTIONS] [NAME]

Arguments:
  [NAME]  Who to greet  [default: (Deadpoolio the amazing's name)]


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.

// See it shows "(Deadpoolio the amazing's name)" instead of the actual default of "Wade Wilson"

Custom help name (metavar)

You can also customize the text used in the generated help text to represent a CLI argument.

By default, it will be the same name you declared, in uppercase letters.

So, if you declare it as:

name: str

It will be shown as:

NAME

But you can customize it with the metavar parameter for typer.Argument().

For example, let's say you don't want to have the default of NAME, you want to have username, in lowercase, and you really want ✨ emojis ✨ everywhere:

import typer


def main(name: str = typer.Argument("World", metavar="✨username✨")):
    typer.echo(f"Hello {name}")


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

Now the generated help text will have ✨username✨ instead of NAME:

$ python main.py --help

Usage: main.py [OPTIONS] ✨username✨

Arguments:
  ✨username✨  [default: World]

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.

Hide a CLI argument from the help text

If you want, you can make a CLI argument not show up in the Arguments section in the help text.

You will probably not want to do this normally, but it's possible:

import typer


def main(name: str = typer.Argument("World", hidden=True)):
    """
    Say hi to NAME very gently, like Dirk.
    """
    typer.echo(f"Hello {name}")


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

Check it:

$ python main.py --help

// Notice there's no Arguments section at all 🔥
Usage: main.py [OPTIONS] [NAME]

  Say hi to NAME very gently, like Dirk.

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.

Info

Have in mind that the CLI argument will still show up in the first line with Usage.

But it won't show up in the main help text under the Arguments section.

Help text for CLI arguments in Click

Click itself doesn't support adding help for CLI arguments, and it doesn't generate help for them as in the "Arguments:" sections in the examples above.

Not supporting help in CLI arguments is an intentional design decision in Click:

This is to follow the general convention of Unix tools of using arguments for only the most necessary things, and to document them in the command help text by referring to them by name.

So, in Click applications, you are expected to write all the documentation for CLI arguments by hand in the docstring.


Nevertheless, Typer supports help for CLI arguments. ✨ 🤷‍♂

Typer doesn't follow that convention and instead supports help to make it easier to have consistent help texts with a consistent format for your CLI programs. 🎨

This is also to help you create CLI programs that are ✨ awesome ✨ by default. With very little code.

If you want to keep Click's convention in a Typer app, you can do it with the hidden parameter as described above.

Technical Details

To support help in CLI arguments Typer does a lot of internal work in its own sub-classes of Click's internal classes.