[issue33190] problem with ABCMeta.__prepare__ when called after types.new_class
Ivan Levkivskyi
report at bugs.python.org
Fri Mar 30 17:02:10 EDT 2018
Ivan Levkivskyi <levkivskyi at gmail.com> added the comment:
This is not a bug, but a misunderstanding:
* First, ABCMeta doesn't have `__prepare__`, it is just `type.__prepare__`
* Second, the third argument to `types.new_class` is called `kwds` for a reason. It is not a namespace like in `type` but the set of keywords in the equivalent class definition. For example:
types.new_class('Test', (A, B), {'metaclass': Meta, 'foo': 42})
id equivalent to
class Test(A, B, metaclass=Meta, foo=42):
pass
If you want to populate the namespace, then you should use the fourth argument `exec_body` which should be a callable that takes newly created dictionary and populates it with items. For your case it should be:
C = new_class("C", (MyABC,), {}, exec_body=lambda ns: ns.update(namespace))
If you want to clarify the corresponding docstring, then please open a PR. Otherwise you can close the issue.
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<https://bugs.python.org/issue33190>
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