Signature-based Function Overloading in Python

[Bruno Desthuilliers]

Michael Rudolf a écrit :
(snip)
> (pseudocode - this is *not* python ;)
> 
> class Machines (Object):
>     @classmethod
>     def shutdown(cls, Machine, emergency=False):
>        try:
>         if Machine is instanceof(Fileservers):


>             if not emergency:
>                 Machine.unmount_raid_first()
>                 ...
>             Machine.halt()
>         if Machine is instanceof(Router):
>             if not emergency:
>                 cls.shutdown(Machine.attachedmachines)
>             ...
>         ...
>         finally:
>         if emergency and Machine has powerswitch:
>             Machine.powerswitch.Off()
>     @classmethod
>     def emergency(cls):
>         for machine in cls.instances:
>             cls.shutdown(machine, 1)
> 

> One could say that the machines have to know how to shut down itself, 

Indeed !-)

> but there might be dependencies they do not know about,

Then it's the "Machines" (or a "MachineShutdownProtocol" or whatever) 
responsability to manage correct operation order, and you need an API to 
allow communication between the Machine objects and the WhateverItsName 
object in charge of monitoring the process.

All this if you do care about correct OO design, of course - as far as 
I'm concerned, practicallity beats purity !-)

> and as said, it 
> clutters the emergency protocol all over the modules.

Tradeoff, tradeoff. The above won't work for a "plug&play" system.

> There are cases where *no* solution is perfect,

There is always at least one "less worse" solution, depending on the 
concrete use case.