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74 lines
2.3 KiB
ReStructuredText
74 lines
2.3 KiB
ReStructuredText
Writing custom providers
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------------------------
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List of *Objects* providers could be widened with custom providers.
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Below are some tips and recommendations that have to be met:
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1. Every custom provider has to extend base provider class -
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``objects.providers.Provider``.
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2. Cusom provider's ``__init__()`` could be overriden with only condition:
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parent initializer (``objects.providers.Provider.__init__()``) has
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to be called.
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3. Providing strategy has to be implemented in custom provider's
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``_provide()`` method. All ``*args`` & ``**kwargs`` that will be
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recieved by ``objects.providers.Provider.__call__()`` will be transefed
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to custom provider's ``_provide()``.
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4. If custom provider is based on some standard providers, it is better to
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use delegation of standard providers, then extending of them.
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5. If custom provider defines any attributes, it is good to list them in
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``__slots__`` attribute (as *Objects* does). It can save some memory.
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6. If custom provider deals with injections (e.g. ``Factory``,
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``Singleton`` providers), it is strongly recommended to use
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``objects.injections.Injection`` and its subclasses:
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``objects.injections.KwArg``, ``objects.injections.Attribute`` and
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``objects.injections.Method``.
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Example:
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.. image:: /images/providers/custom_provider.png
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:width: 100%
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:align: center
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.. code-block:: python
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"""Custom `Factory` example."""
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from objects.providers import Provider
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from objects.providers import Factory
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class User(object):
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"""Example class User."""
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class UsersFactory(Provider):
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"""Example users factory."""
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__slots__ = ('_factory',)
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def __init__(self):
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"""Initializer."""
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self._factory = Factory(User)
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super(UsersFactory, self).__init__()
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def _provide(self, *args, **kwargs):
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"""Return provided instance."""
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return self._factory(*args, **kwargs)
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# Users factory:
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users_factory = UsersFactory()
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# Creating several User objects:
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user1 = users_factory()
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user2 = users_factory()
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# Making some asserts:
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assert isinstance(user1, User)
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assert isinstance(user2, User)
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assert user1 is not user2
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