Add support for custom parameter types about typer HOT 10 CLOSED

@ananis25 I think a nice approach would be to register custom types with a new function - either on typer or a typer.Typer object:

import typer
typer.register_type(datetime.date, lambda string: datetime.datetime.strptime(string, '%Y-%m-%d').date())

import typer
app = typer.Typer()
app.register_type(datetime.date, lambda string: datetime.datetime.strptime(string, '%Y-%m-%d').date())

typer.main.get_click_type would then check an internal store of registered types before its default behaviour.
For bonus points, allow multiple deserializing functions to be tried in order. They could be specified as a list to register_type, or multiple calls to register_type

from typer.

I agree with the solution proposed by @jackric.
Also, to add on top of that:

There are lots of "wrapper types" that can be called on a string input and give an augmented object that is still a string. Many more are just variants of already handled types.

So maybe if Typer did just try to call the annotated type by default, it would be a quick and easy way to solve many problems with not so much work.
It could even be enabled (or disabled) with an option in the Typer instanciation. In case some users somehow expect to get an error on unhandled types.

--

I think it should at least be possible to skip an unhandled type with a mere warning. To let users properly annotate their functions without having to use some crazy black magic.

from typer.

I need this feature (actually for datetime.date like your example) - so please make PR!

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Hey @jackric, the method used above requires a global container, which makes me uneasy. You could probably use this snippet in your code and import the typer module from it.

from typer.

If I understand correctly, the above snippet does exactly this, isn't it? I'd leave it to the maintainers to see if they really want to add this.

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One thing that is missing when registering custom types (or at least not explicitly clear) is the usage when I just want to add a converter to an existing type. For example - parsing a hexadecimal number. I want to extend the parsing, but the result type is still a number.

The options I see for this are either:

@app.command()
def command(number: int = Typer.Argument(converter=lambda x: int(x, 0)))

Or

class HexInt(int): pass

# Fill in registering custom type

@app.command()
def command(number: HexInt)

I am not sure what I think about either.

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My 2 cents: declaring the HexInt class/type feels wrong, because later the type system says number is HexInt, when we really want to think of it as an int.

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I wrote a PR that implements this, please let me know what you think: #443

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+1 would love to see @paulo-raca 's PR merged. Thanks!

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Thanks all! Support for this was added in #583, the new docs are here: https://typer.tiangolo.com/tutorial/parameter-types/custom-types/, it's available in Typer 0.8.0, just released. 🎉

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