Make inject decorator work also on classes and save some keystrokes

README.rst

@@ -32,10 +32,8 @@ We'll use an in-memory SQLite database for our example::
 
 And make up an imaginary RequestHandler class that uses the SQLite connection::
 
-    >>> class RequestHandler(object):
-    ...   @inject(db=sqlite3.Connection)
-    ...   def __init__(self, db):
-    ...     self._db = db
+    >>> @inject(_db=sqlite3.Connection)
+    ... class RequestHandler(object):
     ...   def get(self):
     ...     cursor = self._db.cursor()
     ...     cursor.execute('SELECT key, value FROM data ORDER by key')
@@ -236,6 +234,20 @@ constructor of a normal class::
     ...     def describe(self, name):
     ...         return '%s is a man of astounding insight' % name
 
+You can also ``inject``-decorate class itself. This code::
+
+    >>> @inject(name=Name)
+    ... class Item(object):
+    ...     pass
+
+is equivalent to::
+
+    >>> class Item(object):
+    ...     @inject(name=Name)
+    ...     def __init__(self, name):
+    ...         self.name = name
+
+
 Injector
 --------
 The ``Injector`` brings everything together. It takes a list of
@@ -278,9 +290,9 @@ constructors. Let's have for example::
     ...     def __init__(self, name):
     ...         self.name = name
 
+    >>> @inject(db=Database)
     >>> class UserUpdater(object):
-    ...     @inject(db = Database)
-    ...     def __init__(self, db, user):
+    ...     def __init__(self, user):
     ...         pass 
 
 You may want to have database connection ``db`` injected into ``UserUpdater`` constructor,
@@ -303,10 +315,10 @@ using all of them.
 ``AssistedBuilder(X)`` is injectable just as anything else, if you need instance of it you
 just ask for it like that::
 
-    >>> class NeedsUserUpdater(object):
-    ...     @inject(builder=AssistedBuilder(UserUpdater))
-    ...     def method(self, builder):
-    ...         pass
+    >>> @inject(updater_builder=AssistedBuilder(UserUpdater))
+    ... class NeedsUserUpdater(object):
+    ...     def method(self):
+    ...         updater = self.updater_builder.build(user=None)
 
 More information on this topic:
 

injector.py

@@ -641,7 +641,7 @@ def inject(**bindings):
     'Get my friends'
     """
 
-    def wrapper(f):
+    def method_wrapper(f):
         for key, value in bindings.items():
             bindings[key] = BindingKey(value, None)
         if hasattr(inspect, 'getfullargspec'):
@@ -674,7 +674,24 @@ def inject(**bindings):
             inject = f
         inject.__bindings__ = bindings
         return inject
-    return wrapper
+
+    def class_wrapper(cls):
+        orig_init = cls.__init__
+        @inject(**bindings)
+        def init(self, *args, **kwargs):
+            for key in bindings:
+                setattr(self, key, kwargs.pop(key))
+            orig_init(self, *args, **kwargs)
+        cls.__init__ = init
+        return cls
+
+    def multi_wrapper(something):
+        if type(something) is type:
+            return class_wrapper(something)
+        else:
+            return method_wrapper(something)
+
+    return multi_wrapper
 
 
 class BaseAnnotation(object):

injector_test.py

@@ -735,3 +735,66 @@ class TestThreadSafety(object):
         self.injector.binder.bind(self.cls, scope=singleton)
         a, b = self.gather_results(2)
         assert (a is b)
+
+class TestClassInjection(object):
+    def setup(self):
+        class A(object):
+            counter = 0
+
+            def __init__(self):
+                A.counter += 1
+
+        @inject(a=A)
+        class B(object):
+            pass
+
+        @inject(a=A)
+        class C(object):
+            def __init__(self, noninjectable):
+                self.noninjectable = noninjectable
+
+        self.injector = Injector()
+        self.A = A
+        self.B = B
+        self.C = C
+
+    def test_instantiation_still_requires_parameters(self):
+        for cls in (self.B, self.C):
+            with pytest.raises(Exception):
+                obj = cls()
+
+        with pytest.raises(Exception):
+            c = self.C(noninjectable=1)
+
+        with pytest.raises(Exception):
+            c = self.C(a=self.A())
+
+    def test_injection_works(self):
+        b = self.injector.get(self.B)
+        a = b.a
+        assert (type(a) == self.A)
+
+    def test_assisted_injection_works(self):
+        builder = self.injector.get(AssistedBuilder(self.C))
+        c = builder.build(noninjectable=5)
+
+        assert((type(c.a), c.noninjectable) == (self.A, 5))
+
+    def test_members_are_injected_only_once(self):
+        b = self.injector.get(self.B)
+        _1 = b.a
+        _2 = b.a
+        assert (self.A.counter == 1 and _1 is _2)
+
+    def test_each_instance_gets_new_injection(self):
+        count = 3
+        objs = [self.injector.get(self.B).a for i in range(count)]
+
+        assert (self.A.counter == count)
+        assert (len(set(objs)) == count)
+
+    def test_members_can_be_overwritten(self):
+        b = self.injector.get(self.B)
+        b.a = 123
+
+        assert (b.a == 123)