ansible/docs/docsite/rst/dev_guide/testing/sanity/metaclass-boilerplate.rst

Sanity Tests » metaclass-boilerplate
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Most Python files should include the following boilerplate at the top of the file, right after the
comment header and ``from __future__ import``:

.. code-block:: python

    __metaclass__ = type


Python 2 has "new-style classes" and "old-style classes" whereas Python 3 only has new-style classes.
Adding the ``__metaclass__ = type`` boilerplate makes every class defined in that file into
a new-style class as well.

.. code-block:: python

    from __future__ import absolute_import, division, print_function
    __metaclass__ = type

    class Foo:
        # This is a new-style class even on Python 2 because of the __metaclass__
        pass