class — Expert Playground

Defines a new class (blueprint for creating objects)

Python Playground

class ValidatedMeta(type):
    def __new__(mcs, name, bases, namespace):
        # Require all public methods to have docstrings
        for key, value in namespace.items():
            if callable(value) and not key.startswith("_"):
                if not getattr(value, "__doc__", None):
                    raise TypeError(
                        f"{name}.{key}() must have a docstring"
                    )
        return super().__new__(mcs, name, bases, namespace)

class API(metaclass=ValidatedMeta):
    def get_users(self):
        """Fetch all users."""
        return []

    def get_orders(self):
        """Fetch all orders."""
        return []

print(f"API created with metaclass: {type(API)}")
print(f"Methods: {[m for m in dir(API) if not m.startswith('_')]}")

try:
    class BadAPI(metaclass=ValidatedMeta):
        def no_docs(self):  # missing docstring
            pass
except TypeError as e:
    print(f"Metaclass rejected: {e}")

Output

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Metaclasses control how classes themselves are created. type is the default metaclass. Custom metaclasses can enforce coding standards, register classes, or inject behavior at class definition time.

Challenge

Try modifying the code above to explore different behaviors. Can you extend the example to handle a new use case?

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