bpo-32946: Speed up "from ... import ..." from non-packages. (GH-5873)

Lib/importlib/_bootstrap.py

@@ -1016,31 +1016,30 @@ def _handle_fromlist(module, fromlist, import_, *, recursive=False):
     """
     # The hell that is fromlist ...
     # If a package was imported, try to import stuff from fromlist.
-    if hasattr(module, '__path__'):
-        for x in fromlist:
-            if not isinstance(x, str):
-                if recursive:
-                    where = module.__name__ + '.__all__'
-                else:
-                    where = "``from list''"
-                raise TypeError(f"Item in {where} must be str, "
-                                f"not {type(x).__name__}")
-            elif x == '*':
-                if not recursive and hasattr(module, '__all__'):
-                    _handle_fromlist(module, module.__all__, import_,
-                                     recursive=True)
-            elif not hasattr(module, x):
-                from_name = '{}.{}'.format(module.__name__, x)
-                try:
-                    _call_with_frames_removed(import_, from_name)
-                except ModuleNotFoundError as exc:
-                    # Backwards-compatibility dictates we ignore failed
-                    # imports triggered by fromlist for modules that don't
-                    # exist.
-                    if (exc.name == from_name and
-                        sys.modules.get(from_name, _NEEDS_LOADING) is not None):
-                        continue
-                    raise
+    for x in fromlist:
+        if not isinstance(x, str):
+            if recursive:
+                where = module.__name__ + '.__all__'
+            else:
+                where = "``from list''"
+            raise TypeError(f"Item in {where} must be str, "
+                            f"not {type(x).__name__}")
+        elif x == '*':
+            if not recursive and hasattr(module, '__all__'):
+                _handle_fromlist(module, module.__all__, import_,
+                                 recursive=True)
+        elif not hasattr(module, x):
+            from_name = '{}.{}'.format(module.__name__, x)
+            try:
+                _call_with_frames_removed(import_, from_name)
+            except ModuleNotFoundError as exc:
+                # Backwards-compatibility dictates we ignore failed
+                # imports triggered by fromlist for modules that don't
+                # exist.
+                if (exc.name == from_name and
+                    sys.modules.get(from_name, _NEEDS_LOADING) is not None):
+                    continue
+                raise
     return module
 
 
@@ -1102,8 +1101,10 @@ def __import__(name, globals=None, locals=None, fromlist=(), level=0):
             # Slice end needs to be positive to alleviate need to special-case
             # when ``'.' not in name``.
             return sys.modules[module.__name__[:len(module.__name__)-cut_off]]
-    else:
+    elif hasattr(module, '__path__'):
         return _handle_fromlist(module, fromlist, _gcd_import)
+    else:
+        return module
 
 
 def _builtin_from_name(name):

Misc/NEWS.d/next/Core and Builtins/2018-02-25-10-52-40.bpo-32946.Lo09rG.rst

+Importing names from already imported module with "from ... import ..." is
+now 30% faster if the module is not a package.

Python/import.c

@@ -1800,10 +1800,21 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
         }
     }
     else {
-        final_mod = _PyObject_CallMethodIdObjArgs(interp->importlib,
-                                                  &PyId__handle_fromlist, mod,
-                                                  fromlist, interp->import_func,
-                                                  NULL);
+        _Py_IDENTIFIER(__path__);
+        PyObject *path;
+        if (_PyObject_LookupAttrId(mod, &PyId___path__, &path) < 0) {
+            goto error;
+        }
+        if (path) {
+            Py_DECREF(path);
+            final_mod = _PyObject_CallMethodIdObjArgs(
+                        interp->importlib, &PyId__handle_fromlist,
+                        mod, fromlist, interp->import_func, NULL);
+        }
+        else {
+            final_mod = mod;
+            Py_INCREF(mod);
+        }
     }
 
   error: