Is it dangeous when using custom metaclass?

[dieter]

jfong at ms4.hinet.net writes:
> Gregory Ewing at 2018/10/16 UTC+8 PM 2:01:01 wrote
>> jfong at ms4.hinet.net wrote:
>> > class Structure(metaclass=StructureMeta): ...
>> > 
>> > class PolyHeader(Structure): ...
>> > 
>> > As my understanding, the metaclass's __init__ was called when a class was
>> > created. In the above example, both the Structure and PolyHeader called it.
>> > My question is: because the PolyHeader inherited Structure, is it reasonable
>> > for PolyHeader to call this __init__ again? Will it cause any possible
>> > trouble?
>> 
>> It's reasonable for both to call it, because they're distinct
>> instances of StructureMeta, each of which need to be initialised.
>
> The PolyHeader is already initialized by inheritance. Is there any way to bypass this __init__?

If there were any, you should find it described in metaclass related documentation.

Likely, you can ensure that followup calls of "__init__" effectively
behave as "no-op"s: let the first call place a marker in the initialized
object and check in later calls whether it is already there.