Loads an extension.

        An extension is a python module that contains commands, cogs, or
        listeners.

        An extension must have a global function, ``setup`` defined as
        the entry point on what to do when the extension is loaded. This entry
        point must have a single argument, the ``bot``.

        Parameters
        ------------
        name: :class:`str`
            The extension name to load. It must be dot separated like
            regular Python imports if accessing a sub-module. e.g.
            ``foo.test`` if you want to import ``foo/test.py``.

        Raises
        --------
        ExtensionNotFound
            The extension could not be imported.
        ExtensionAlreadyLoaded
            The extension is already loaded.
        NoEntryPointError
            The extension does not have a setup function.
        ExtensionFailed
            The extension setup function had an execution error.

def load_extension(self, name):
        """Loads an extension.

        An extension is a python module that contains commands, cogs, or
        listeners.

        An extension must have a global function, ``setup`` defined as
        the entry point on what to do when the extension is loaded. This entry
        point must have a single argument, the ``bot``.

        Parameters
        ------------
        name: :class:`str`
            The extension name to load. It must be dot separated like
            regular Python imports if accessing a sub-module. e.g.
            ``foo.test`` if you want to import ``foo/test.py``.

        Raises
        --------
        ExtensionNotFound
            The extension could not be imported.
        ExtensionAlreadyLoaded
            The extension is already loaded.
        NoEntryPointError
            The extension does not have a setup function.
        ExtensionFailed
            The extension setup function had an execution error.
        """

        if name in self.__extensions:
            raise errors.ExtensionAlreadyLoaded(name)

        try:
            lib = importlib.import_module(name)
        except ImportError as e:
            raise errors.ExtensionNotFound(name, e) from e
        else:
            self._load_from_module_spec(lib, name)