ExtensionArray isin

[TomAugspurger]

Some (many?) extension array scalar types will have a corresponding container type. For example, IPArray defines isin to match the standard library's behavior where an address can be in a network.

https://github.com/ContinuumIO/cyberpandas/blob/054d3a37fe84a8d222795c31bbf99ef34be90fbf/cyberpandas/ip_array.py#L349-L388

Do we want to dispatch isin to Extension arrays? #20522 is doing some work so that pd.core.algos(categorical) dispatches to a specialized (faster) .isin, so the additional work will be small.

[TomAugspurger]

@Ma3aXaKa if you want to take a look at this, it should be pretty straightforward now that you did #20522.

[bourbaki]

Sure. I will look at this.

[jbrockmendel]

I think of ser.isin(vals) as effectively Series([any(x == y for y in vals) for x in ser], index=ser.index). IIUC the IPArray example would have a pretty different semantic meaning, wouldn't it?

[jbrockmendel]

There is now an ExtensionArray.isin; closing.