Added lazy_import to graphene. Fixed #316

Author: syrusakbary

graphene/__init__.py

@@ -43,6 +43,7 @@
         PageInfo
     )
     from .utils.resolve_only_args import resolve_only_args
+    from .utils.module_loading import lazy_import
 
     __all__ = [
         'AbstractType',
@@ -72,4 +73,6 @@
         'ClientIDMutation',
         'Connection',
         'ConnectionField',
-        'PageInfo']
+        'PageInfo',
+        'lazy_import',
+    ]

graphene/utils/module_loading.py

@@ -0,0 +1,26 @@
+from functools import partial
+from importlib import import_module
+
+
+def import_string(dotted_path):
+    """
+    Import a dotted module path and return the attribute/class designated by the
+    last name in the path. Raise ImportError if the import failed.
+    """
+    try:
+        module_path, class_name = dotted_path.rsplit('.', 1)
+    except ValueError as err:
+        raise ImportError("%s doesn't look like a module path" % dotted_path)
+
+    module = import_module(module_path)
+
+    try:
+        return getattr(module, class_name)
+    except AttributeError as err:
+        raise ImportError('Module "%s" does not define a "%s" attribute/class' % (
+            module_path, class_name)
+        )
+
+
+def lazy_import(dotted_path):
+    return partial(import_string, dotted_path)

graphene/utils/tests/test_module_loading.py

@@ -0,0 +1,29 @@
+from pytest import raises
+
+from graphene import String
+from ..module_loading import lazy_import, import_string
+
+
+def test_import_string():
+    MyString = import_string('graphene.String')
+    assert MyString == String
+
+
+def test_import_string_module():
+    with raises(Exception) as exc_info:
+        import_string('graphenea')
+
+    assert str(exc_info.value) == 'graphenea doesn\'t look like a module path'
+
+
+def test_import_string_class():
+    with raises(Exception) as exc_info:
+        import_string('graphene.Stringa')
+
+    assert str(exc_info.value) == 'Module "graphene" does not define a "Stringa" attribute/class'
+
+
+def test_lazy_import():
+    f = lazy_import('graphene.String')
+    MyString = f()
+    assert MyString == String