Move fetch_cls_init() to utils module

dependency_injector/injections.py

@@ -1,7 +1,5 @@
 """Injections module."""
 
-import sys
-
 import six
 
 from .utils import is_provider
@@ -9,17 +7,11 @@ from .utils import is_delegated_provider
 from .utils import is_injection
 from .utils import is_arg_injection
 from .utils import is_kwarg_injection
+from .utils import fetch_cls_init
 
 from .errors import Error
 
 
-_IS_PYPY = '__pypy__' in sys.builtin_module_names
-if _IS_PYPY or six.PY3:  # pragma: no cover
-    _OBJECT_INIT = six.get_unbound_function(object.__init__)
-else:  # pragma: no cover
-    _OBJECT_INIT = None
-
-
 @six.python_2_unicode_compatible
 class Injection(object):
     """Base injection class.
@@ -225,7 +217,13 @@ def inject(*args, **kwargs):
         """Dependency injection decorator."""
         if isinstance(callback_or_cls, six.class_types):
             cls = callback_or_cls
-            cls.__init__ = decorator(_fetch_cls_init(cls))
+            cls_init = fetch_cls_init(cls)
+            if not cls_init:
+                raise Error(
+                    'Class {0}.{1} has no __init__() '.format(cls.__module__,
+                                                              cls.__name__) +
+                    'method and could not be decorated with @inject decorator')
+            cls.__init__ = decorator(cls_init)
             return cls
 
         callback = callback_or_cls
@@ -256,19 +254,6 @@ def inject(*args, **kwargs):
     return decorator
 
 
-def _fetch_cls_init(cls):
-    """Return reference to the class.__init__() method if it is defined."""
-    try:
-        cls_init = six.get_unbound_function(cls.__init__)
-        assert cls_init is not _OBJECT_INIT
-    except (AttributeError, AssertionError):
-        raise Error(
-            'Class {0}.{1} has no __init__() '.format(cls.__module__,
-                                                      cls.__name__) +
-            'method and could not be decorated with @inject decorator')
-    return cls_init
-
-
 def _parse_args_injections(args):
     """Parse positional argument injections according to current syntax."""
     return tuple(Arg(arg) if not is_injection(arg) else arg

dependency_injector/utils.py

@@ -1,5 +1,6 @@
 """Utils module."""
 
+import sys
 import threading
 
 import six
@@ -13,6 +14,12 @@ GLOBAL_LOCK = threading.RLock()
 :type: :py:class:`threading.RLock`
 """
 
+_IS_PYPY = '__pypy__' in sys.builtin_module_names
+if _IS_PYPY or six.PY3:  # pragma: no cover
+    _OBJECT_INIT = six.get_unbound_function(object.__init__)
+else:  # pragma: no cover
+    _OBJECT_INIT = None
+
 
 def is_provider(instance):
     """Check if instance is provider instance.
@@ -220,3 +227,21 @@ def represent_provider(provider, provides):
                            provider.__class__.__name__)),
         provides=repr(provides) if provides is not None else '',
         address=hex(id(provider)))
+
+
+def fetch_cls_init(cls):
+    """Return reference to the class.__init__() method if it is defined.
+
+    :param cls: Class instance
+    :type cls: type
+
+    :return: Reference to the class.__init__() if any, or None otherwise.
+    :rtype: unbound method | None
+    """
+    try:
+        cls_init = six.get_unbound_function(cls.__init__)
+        assert cls_init is not _OBJECT_INIT
+    except (AttributeError, AssertionError):
+        return None
+    else:
+        return cls_init