CODEWITHSUNDEEP
pythonmetaclass
Ivan Kalita
Ivan Kalita

Reputation: 2287

Built-in classes metaclass in Python

Are there any built-in Python classes that are not instances of type metaclass?

>>> type(list)
<type 'type'>
>>> type(dict)
<type 'type'>
>>> type(some_builtin_python_class)
<type 'some_type_other_than_type'>

Upvotes: 2

Views: 233

Answers (1)

abarnert
abarnert

Reputation: 366003

Depends what you mean by "built-in". If you mean any of the C-implemented (in CPython) classes exposed as builtins (and in builtin), then no, none of them have a different metaclass.*

But there are definitely classes in the stdlib that do. For example:

>>> type(collections.abc.Iterable)
abc.ABCMeta

To clarify: Other metaclasses are of course subclasses of type, so, by the normal inheritance rules, it's still true that isinstance(Iterable, type)—but it's not true that type(Iterable) == type. Which is what you were asking for in your question—a type for which type(T) returns <type 'some_type_other_than_type'>.

* Not in 3.x, at any rate. Things were different in 2.x, where there were classic classes, and, once upon a time, "fake classes" that were actually functions that looked like type instances but weren't, and returned instances of a hidden type instance when called.

Upvotes: 4

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