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Observer pattern

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技术栈
python
领域
backend

调研方向

从 switch.py 和 issue 中展示的 Widget/YDoc 实现开始,然后查看 psygnal 和 traitlets 如何表示被观察的属性。确定可行的 observer 设计是否涵盖 YMap 值条目和嵌套的 YDoc 结构。完成的标准是确定一致认可的实现范围,并明确观察这些结构的方法。

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描述

In https://github.com/jupyter-widgets/ipywidgets/issues/3293#issuecomment-1433848240 @tlambert03 mentioned psygnal, that could be used to implement the equivalent of traitlets.
I think it is a good idea, but I'm not sure how it could fit here. For instance, take the Switch model, currently implemented as:

from .ypywidgets import Widget


class Switch(Widget):

    def __init__(self, value: bool = False, open_comm: bool = True) -> None:
        super().__init__(name="switch", open_comm=open_comm)
        self.yvalue = self.ydoc.get_map("value")
        self._set(value)

    def _set(self, value: bool) -> None:
        with self.ydoc.begin_transaction() as t:
            self.yvalue.set(t, "value",  value)

    @property
    def value(self) -> bool:
        return self.yvalue["value"]

    @value.setter
    def value(self, value: bool):
        if value == self.value:
            return

        self._set(value)

    def toggle(self):
        self.value = not self.value

Its YDoc consists of a YMap named value, with a single entry in it, also named value, which contains the boolean value of the switch. Here the observer pattern is manually implemented using a getter and a setter function for the value attribute.
If we were to use psygnal, we would need a way to point to the YDoc's structure (self.yvalue and value entry in it) from the psygnal's attribute.
I think that's the reason why traitlets use Python's descriptor protocol, which allows to get the name of an attribute at runtime.
Also, I'm not sure how we could connect nested YDoc structures (e.g. a YMap can contain other Y structures), but I don't think it was possible with traitlets anyway, so that would be an improvement.

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