version 0.2.0, external dependency provider has been added

README.md

@@ -172,3 +172,62 @@ assert isinstance(a2, ObjectAMock)
 assert a1 is not a2
 assert a1.db is a2.db is Catalog.database()
 ```
+
+Example of objects catalog external dependency:
+
+```python
+"""
+Concept example of objects catalogs.
+"""
+
+from objects import AbstractCatalog
+from objects.providers import Singleton, NewInstance, ExternalDependency
+from objects.injections import InitArg, Attribute
+import sqlite3
+
+
+# Some example classes.
+class ObjectA(object):
+    def __init__(self, db):
+        self.db = db
+
+
+class ObjectB(object):
+    def __init__(self, a, db):
+        self.a = a
+        self.db = db
+
+
+# Catalog of objects providers.
+class Catalog(AbstractCatalog):
+    """
+    Objects catalog.
+    """
+
+    database = ExternalDependency(instance_of=sqlite3.Connection)
+    """ :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 """
+
+
+# Satisfaction of external dependency.
+Catalog.database.satisfy(Singleton(sqlite3.Connection,
+                                   InitArg('database', ':memory:'),
+                                   Attribute('row_factory', sqlite3.Row)))
+
+# Catalog static provides.
+a1, a2 = Catalog.object_a(), Catalog.object_a()
+b1, b2 = Catalog.object_b(), Catalog.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 is Catalog.database()
+```

VERSION

@@ -1 +1 @@
-0.1.0
+0.2.0

examples/external_dependency.py

@@ -0,0 +1,54 @@
+"""
+Concept example of objects catalogs.
+"""
+
+from objects import AbstractCatalog
+from objects.providers import Singleton, NewInstance, ExternalDependency
+from objects.injections import InitArg, Attribute
+import sqlite3
+
+
+# Some example classes.
+class ObjectA(object):
+    def __init__(self, db):
+        self.db = db
+
+
+class ObjectB(object):
+    def __init__(self, a, db):
+        self.a = a
+        self.db = db
+
+
+# Catalog of objects providers.
+class Catalog(AbstractCatalog):
+    """
+    Objects catalog.
+    """
+
+    database = ExternalDependency(instance_of=sqlite3.Connection)
+    """ :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 """
+
+
+# Satisfaction of external dependency.
+Catalog.database.satisfy(Singleton(sqlite3.Connection,
+                                   InitArg('database', ':memory:'),
+                                   Attribute('row_factory', sqlite3.Row)))
+
+# Catalog static provides.
+a1, a2 = Catalog.object_a(), Catalog.object_a()
+b1, b2 = Catalog.object_b(), Catalog.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 is Catalog.database()

objects/providers.py

@@ -108,6 +108,44 @@ class Singleton(NewInstance):
         return self.instance
 
 
+class ExternalDependency(Provider):
+    """
+    External dependency provider.
+    """
+
+    def __init__(self, instance_of):
+        """
+        Initializer
+
+        :param instance_of: type
+        """
+        self.instance_of = instance_of
+        self.dependency = None
+        super(ExternalDependency, self).__init__()
+
+    def satisfy(self, provider):
+        """
+        Satisfies an external dependency.
+
+        :param provider: Provider
+        """
+        self.dependency = provider
+
+    def __call__(self, *args, **kwargs):
+        """
+        Returns provided instance.
+        """
+        if not self.dependency:
+            raise ValueError('Dependency is not satisfied')
+
+        result = self.dependency.__call__(*args, **kwargs)
+
+        if not isinstance(result, self.instance_of):
+            raise TypeError('{} is not an instance of {}'.format(result,
+                                                                 self.instance_of))
+        return result
+
+
 class _StaticProvider(Provider):
     """
     Static provider is base implementation that provides exactly the same as