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about types.new_class and module


On 2019-03-04 18:02, Jimmy Girardet wrote:
> Hello,
> 
> I'm looking for an explanation where live classes created by
> types.new_class() :
> 
> py> import types
> 
> py> types.new_class('A')
> 
> types.A
> 
> py> types.A
> 
> AttributeError: module 'types' has no attribute 'A'
> 
> py> _.__module__
> 
> 'types'
> 
> 
> The new class comes from `types` module without being inside.
> 
> That's annoying to me for my use case :
> 
> I'm trying to create dataclasses on the fly using? make_dataclass (which
> uses types.new_class). For new created classes, I have a cache to not
> recreate twice the same class.
> 
> But I want to be sure not to override an existing class somewhere in the
> namespace which is already 'types.MyNewclass'. but how to check it if
> it's not in types ?
> 
> To be clear :
> 
> make_dataclass('Bla', {}) should raise an error if something named
> 'types.Bla' already exists.
> 
> I hope I'm clear enough.
> 
'new_class' creates a new class with the given name and returns a 
reference to it.

The class doesn't 'live' anywhere.

Although you might /think/ that an object lives in a certain namespace, 
it's just that there's a name there that's bound to the object.

You can, in fact, create 2 classes with the same name.

 >>> import types
 >>> t1 = types.new_class('A')
 >>> t2 = types.new_class('A')
 >>> t1 is t2
False