Merge pull request #442 from blakegong/features/add-dotted-arguments-for-lazy-import

Improve lazy_import() to accept dotted_attributes

graphene/utils/module_loading.py

@@ -2,10 +2,13 @@ from functools import partial
 from importlib import import_module
 
 
-def import_string(dotted_path):
+def import_string(dotted_path, dotted_attributes=None):
     """
     Import a dotted module path and return the attribute/class designated by the
-    last name in the path. Raise ImportError if the import failed.
+    last name in the path. When a dotted attribute path is also provided, the
+    dotted attribute path would be applied to the attribute/class retrieved from
+    the first step, and return the corresponding value designated by the
+    attribute path. Raise ImportError if the import failed.
     """
     try:
         module_path, class_name = dotted_path.rsplit('.', 1)
@@ -15,12 +18,27 @@ def import_string(dotted_path):
     module = import_module(module_path)
 
     try:
-        return getattr(module, class_name)
+        result = getattr(module, class_name)
     except AttributeError:
         raise ImportError('Module "%s" does not define a "%s" attribute/class' % (
             module_path, class_name)
         )
 
+    if not dotted_attributes:
+        return result
+    else:
+        attributes = dotted_attributes.split('.')
+        traveled_attributes = []
+        try:
+            for attribute in attributes:
+                traveled_attributes.append(attribute)
+                result = getattr(result, attribute)
+            return result
+        except AttributeError:
+            raise ImportError('Module "%s" does not define a "%s" attribute inside attribute/class "%s"' % (
+                module_path, '.'.join(traveled_attributes), class_name
+            ))
 
-def lazy_import(dotted_path):
-    return partial(import_string, dotted_path)
+
+def lazy_import(dotted_path, dotted_attributes=None):
+    return partial(import_string, dotted_path, dotted_attributes)

graphene/utils/tests/test_module_loading.py

@@ -1,6 +1,7 @@
 from pytest import raises
 
 from graphene import String
+from graphene.types.objecttype import ObjectTypeMeta
 from ..module_loading import lazy_import, import_string
 
 
@@ -8,6 +9,9 @@ def test_import_string():
     MyString = import_string('graphene.String')
     assert MyString == String
 
+    MyObjectTypeMeta = import_string('graphene.ObjectType', '__class__')
+    assert MyObjectTypeMeta == ObjectTypeMeta
+
 
 def test_import_string_module():
     with raises(Exception) as exc_info:
@@ -23,7 +27,31 @@ def test_import_string_class():
     assert str(exc_info.value) == 'Module "graphene" does not define a "Stringa" attribute/class'
 
 
+def test_import_string_attributes():
+    with raises(Exception) as exc_info:
+        import_string('graphene.String', 'length')
+
+    assert str(exc_info.value) == 'Module "graphene" does not define a "length" attribute inside attribute/class ' \
+                                  '"String"'
+
+    with raises(Exception) as exc_info:
+        import_string('graphene.ObjectType', '__class__.length')
+
+    assert str(exc_info.value) == 'Module "graphene" does not define a "__class__.length" attribute inside ' \
+                                  'attribute/class "ObjectType"'
+
+    with raises(Exception) as exc_info:
+        import_string('graphene.ObjectType', '__classa__.__base__')
+
+    assert str(exc_info.value) == 'Module "graphene" does not define a "__classa__" attribute inside attribute/class ' \
+                                  '"ObjectType"'
+
+
 def test_lazy_import():
     f = lazy_import('graphene.String')
     MyString = f()
     assert MyString == String
+
+    f = lazy_import('graphene.ObjectType', '__class__')
+    MyObjectTypeMeta = f()
+    assert MyObjectTypeMeta == ObjectTypeMeta