dynamic drop down acc. to context

[spectereye]

Hi, i want options of state below changed acc. to country user selected,
i see url below mentioned "Generate options based on time or context" - but no idea how to implement it, help please, thanks!
https://offerrall.github.io/FuncToWeb/dropdowns/#use-cases-for-dynamic-dropdowns

STATES = {
    'country1': ['state1', 'state2'],
    'country2': ['state3', 'state4'],
}

def _get_countries():
    return list(STATES)

def _get_states(country):
    return STATES[country]

def population(
        country: Literal[_get_countries],
        state: Literal[_get_states]
):
    """population of state of country"""
    return f'country={country}, state={state}'

run(population)

[offerrall]

Hi! Thanks for using func-to-web!

This isn't currently supported. The issue is that _get_states(country) needs the country parameter, but func-to-web calls it when the form loads - before the user has selected anything.

Why your code doesn't work:

def _get_states(country):  # ❌ Needs parameter
    return STATES[country]

def population(
    country: Literal[_get_countries],
    state: Literal[_get_states]  # ❌ Can't call without argument
):
    ...

Dynamic dropdowns generate options at form load time, not in response to field changes. They can't depend on other fields.

Workaround - Combined field:

from typing import Literal
from func_to_web import run

STATES = {
    'country1': ['state1', 'state2'],
    'country2': ['state3', 'state4'],
}

def _get_pairs():
    return [f"{c} → {s}" for c, states in STATES.items() for s in states]

def population(location: Literal[_get_pairs]):  # type: ignore
    country, state = location.split(' → ')
    return f'country={country}, state={state}'

run(population)

---

I'd like to add support for dependent fields in the future, but I need to figure out the right way to implement it without adding too much complexity. If this feature is important to you, please open a GitHub issue so I can gauge interest and discuss potential approaches!

[spectereye]

thanks! and it's feature needed very commonly, the _get_pairs is not so pythonic :-) and great if there is some way found to implement this. please great this ticket as new feature request too.

[offerrall]

I'm actively working on this feature right now.

v0.9.12

I just added a cleaner syntax for dynamic dropdowns:

from typing import Annotated
from func_to_web.types import Dropdown

def population(
    country: Annotated[str, Dropdown(_get_countries)]
):
    ...

What's next

I'm designing a more powerful solution - not just dependent dropdowns, but function chaining where any field can trigger updates to other fields dynamically.

Still exploring the best approach to make it pythonic, type-safe, and backward compatible.

Target: v0.1.0

I'll update this issue as I make progress.