Argument vs Option

In Typer, there are two primary classes for providing CLI parameter configuration:

  • Argument results in a positional CLI argument.

  • Option results in a keyword CLI argument, preceded with a --.

With more modern python type annotations, this distinction is unnecessary, because parameters (positional or keyword) can be determined directly from the function signature.

Consider the following function signatures:

def pos_or_keyword(a, b):
    pass

def pos_only(a, b, /):
    pass

def keyword_only(*, a, b=2):
    pass

def mixture(a, /, b, *, c=3):
    pass

If you aren't familiar with these declarations, refer to the official PEP570, or a more user-friendly tutorial.

From these function signatures, we can deduce:

  1. Which parameters are position-only, keyword-only, or both.

  2. Which parameters are required, by their lack of defaults.

Because of these builtin python mechanisms, Cyclopts has a single Parameter class used for providing additional parameter metadata.

I believe that Typer's separate Argument and Option classes are a relic from when they must be supplied as a parameter's proxy default value.

app = typer.Typer()

@app.command()
def foo(a=Argument(), b=Option(default=2)):
    pass

When used as such, we lose the ability to define the function signature with position-only or keyword-only markers. We also lose the ability to directly inspect which parameters are optional by having "real" defaults and which ones are required.