python-dependency-injector/examples/usage.py

"""Concept example of objects catalogs."""

from objects import AbstractCatalog

from objects.providers import Singleton
from objects.providers import NewInstance

from objects.injections import InitArg
from objects.injections import Attribute

from objects.errors import Error

import sqlite3


class ObjectA(object):

    """Example class ObjectA, that has dependency on database."""

    def __init__(self, db):
        """Initializer."""
        self.db = db


class ObjectB(object):

    """Example class ObjectB, that has dependencies on ObjectA and database."""

    def __init__(self, a, db):
        """Initializer."""
        self.a = a
        self.db = db


class Catalog(AbstractCatalog):

    """Catalog of objects providers."""

    database = Singleton(sqlite3.Connection,
                         InitArg('database', ':memory:'),
                         Attribute('row_factory', sqlite3.Row))
    """:type: (objects.Provider) -> sqlite3.Connection"""

    object_a = NewInstance(ObjectA,
                           InitArg('db', database))
    """:type: (objects.Provider) -> ObjectA"""

    object_b = NewInstance(ObjectB,
                           InitArg('a', object_a),
                           InitArg('db', database))
    """:type: (objects.Provider) -> ObjectB"""


# Dependencies injection into class.
class Consumer(object):

    """Example consumer class."""

    dependencies = Catalog(Catalog.object_a,
                           Catalog.object_b)

    def example(self):
        """Example method."""
        a1 = self.dependencies.object_a()
        a2 = self.dependencies.object_a()

        b1 = self.dependencies.object_b()
        b2 = self.dependencies.object_b()

        # Some asserts.
        assert a1 is not a2
        assert b1 is not b2
        assert a1.db is a2.db is b1.db is b2.db

        try:
            self.dependencies.database()
        except Error:
            pass
        else:
            raise Exception('Database is not listed as a dependency')


Consumer().example()


# Dependencies injection (The Python Way) into a callback.
def consumer_callback(dependencies=Catalog(Catalog.object_a,
                                           Catalog.object_b)):
    """Example function."""
    a1 = dependencies.object_a()
    a2 = dependencies.object_a()

    b1 = dependencies.object_b()
    b2 = dependencies.object_b()

    # Some asserts.
    assert a1 is not a2
    assert b1 is not b2
    assert a1.db is a2.db is b1.db is b2.db

    try:
        dependencies.database()
    except Error:
        pass
    else:
        raise Exception('Database is not listed as a dependency')