531 Provider import from string (ets-labs#555)

* Implement string imports for Factory, Callable, Singletons, and Resource

* Refactor the implementation

* Add tests

* Update tests to pass on Python 2

* Update typing and add typing tests

* Update changelog

* Update docs

Author: rmk135

docs/main/changelog.rst

@@ -21,6 +21,10 @@ Development version
   ``FactoryAggregate.factories`` attribute.
 - Add ``.set_providers()`` method to the ``FactoryAggregate`` provider. It is an alias for
   ``FactoryAggregate.set_factories()`` method.
+- Add string imports for ``Factory``, ``Singleton``, ``Callable``, ``Resource``, and ``Coroutine``
+  providers, e.g. ``Factory("module.Class")``.
+  See issue `#531 <https://github.com/ets-labs/python-dependency-injector/issues/531>`_.
+  Thanks to `@al-stefanitsky-mozdor <https://github.com/al-stefanitsky-mozdor>`_ for suggesting the feature.
 - Fix ``Dependency`` provider to don't raise "Dependency is not defined" error when the ``default``
   is a falsy value of proper type.
   See issue `#550 <https://github.com/ets-labs/python-dependency-injector/issues/550>`_. Thanks to

docs/providers/factory.rst

@@ -110,6 +110,45 @@ attribute of the provider that you're going to inject.
 
 .. note:: Any provider has a ``.provider`` attribute.
 
+.. _factory-string-imports:
+
+String imports
+--------------
+
+``Factory`` provider can handle string imports:
+
+.. code-block:: python
+
+   class Container(containers.DeclarativeContainer):
+
+       service = providers.Factory("myapp.mypackage.mymodule.Service")
+
+You can also make a relative import:
+
+.. code-block:: python
+
+   # in myapp/container.py
+
+   class Container(containers.DeclarativeContainer):
+
+       service = providers.Factory(".mypackage.mymodule.Service")
+
+or import a member of the current module just specifying its name:
+
+.. code-block:: python
+
+   class Service:
+       ...
+
+
+   class Container(containers.DeclarativeContainer):
+
+       service = providers.Factory("Service")
+
+.. note::
+   ``Singleton``, ``Callable``, ``Resource``, and ``Coroutine`` providers handle string imports
+   the same way as a ``Factory`` provider.
+
 .. _factory-specialize-provided-type:
 
 Specializing the provided type