Maintain receivers order

[pawamoy]

I was able to subclass and patch signals to maintain the order is which receivers are connected:

from __future__ import annotations

from collections import defaultdict
from typing import Hashable

from blinker import NamedSignal


class OrderedSet(dict):
    def __or__(self, other: set | OrderedSet) -> OrderedSet:  # type: ignore[override]
        other_keys = other if isinstance(other, set) else other.keys()
        return OrderedSet.fromkeys(*self.keys(), *other_keys)  # type: ignore[return-value]

    def add(self, value: Hashable) -> None:
        self[value] = None

    def discard(self, value: Hashable) -> None:
        if value in self:
            del self[value]


class Signal(NamedSignal):
    def __init__(self, name: str, doc: str | None = None) -> None:
        super().__init__(name, doc)
        self._by_receiver = defaultdict(OrderedSet)  # type: ignore[arg-type]
        self._by_sender = defaultdict(OrderedSet)  # type: ignore[arg-type]


class Namespace(dict):
    """A mapping of signal names to signals."""

    def signal(self, name: str, doc: str | None = None) -> Signal:
        """Return the `Signal` *name*, creating it if required.

        Repeated calls to this function will return the same signal object.
        """
        try:
            return self[name]
        except KeyError:
            return self.setdefault(name, Signal(name, doc))


signal = Namespace().signal

Import your own signal instead of blinker.signal and receivers order will be maintained 🙂

[davidism]

You can set Signal.set_class = OrderedSet as of Blinker 1.7.

[pawamoy]

Thanks @davidism!