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https://github.com/ets-labs/python-dependency-injector.git
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167 lines
4.6 KiB
ReStructuredText
167 lines
4.6 KiB
ReStructuredText
Providers
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=========
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External dependency providers
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-----------------------------
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``ExternalDependency`` provider can be useful for development of
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self-sufficient libraries / modules / applications, that has required external
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dependencies.
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For example, you have created self-sufficient library / module / application,
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that has dependency on *database connection*.
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Second step you want to do is to make this software component to be easy
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reusable by wide amount of developers and to be easily integrated into many
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applications.
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It may be good idea, to move all external dependencies (like
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*database connection*) to the top level and make them to be injected on your
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software component's initialization. It will make third party developers feel
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themselves free about integration of yours component in their applications,
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because of they would be able to find right place / right way for doing this
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in their application's architectures.
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On the other side,
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you can be sure, that your external dependency will be satisfied by appropriate
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instance.
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Example:
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.. code-block:: python
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"""External dependency providers example."""
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import sqlite3
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from objects.providers import Singleton
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from objects.providers import Factory
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from objects.providers import ExternalDependency
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from objects.injections import KwArg
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from objects.injections import Attribute
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class ObjectA(object):
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"""ObjectA has dependency on database."""
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def __init__(self, database):
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"""Initializer.
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Database dependency need to be injected via init arg."""
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self.database = database
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def get_one(self):
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"""Select one from database and return it."""
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return self.database.execute('SELECT 1').fetchone()[0]
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# Database and `ObjectA` providers.
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database = ExternalDependency(instance_of=sqlite3.Connection)
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object_a_factory = Factory(ObjectA,
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KwArg('database', database))
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# Satisfaction of external dependency.
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database.override(Singleton(sqlite3.Connection,
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KwArg('database', ':memory:'),
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KwArg('timeout', 30),
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KwArg('detect_types', True),
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KwArg('isolation_level', 'EXCLUSIVE'),
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Attribute('row_factory', sqlite3.Row)))
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# Creating several `ObjectA` instances.
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object_a_1 = object_a_factory()
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object_a_2 = object_a_factory()
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# Making some asserts.
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assert object_a_1 is not object_a_2
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assert object_a_1.database is object_a_2.database is database()
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Config providers
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----------------
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Providers delegation
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--------------------
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Overriding of providers
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-----------------------
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Any provider can be overridden by another provider.
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Example:
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.. code-block:: python
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"""Providers overriding example."""
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import sqlite3
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from objects.providers import Factory
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from objects.providers import Singleton
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from objects.injections import KwArg
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from objects.injections import Attribute
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class ObjectA(object):
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"""ObjectA has dependency on database."""
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def __init__(self, database):
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"""Initializer.
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Database dependency need to be injected via init arg."""
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self.database = database
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def get_one(self):
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"""Select one from database and return it."""
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return self.database.execute('SELECT 1')
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class ObjectAMock(ObjectA):
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"""Mock of ObjectA.
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Has no dependency on database.
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"""
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def __init__(self):
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"""Initializer."""
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def get_one(self):
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"""Select one from database and return it.
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Mock makes no database queries and always returns two instead of one.
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"""
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return 2
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# Database and `ObjectA` providers.
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database = Singleton(sqlite3.Connection,
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KwArg('database', ':memory:'),
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KwArg('timeout', 30),
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KwArg('detect_types', True),
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KwArg('isolation_level', 'EXCLUSIVE'),
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Attribute('row_factory', sqlite3.Row))
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object_a_factory = Factory(ObjectA,
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KwArg('database', database))
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# Overriding `ObjectA` provider with `ObjectAMock` provider.
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object_a_factory.override(Factory(ObjectAMock))
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# Creating several `ObjectA` instances.
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object_a_1 = object_a_factory()
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object_a_2 = object_a_factory()
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# Making some asserts.
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assert object_a_1 is not object_a_2
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assert object_a_1.get_one() == object_a_2.get_one() == 2
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