bpo-29851: Have importlib.reload() raise ImportError if the module's spec is not found (GH-972)

Doc/library/importlib.rst

@@ -203,6 +203,9 @@ Functions
    classes.
 
    .. versionadded:: 3.4
+   .. versionchanged:: 3.7
+       :exc:`ModuleNotFoundError` is raised when the module being reloaded lacks
+       a :class:`ModuleSpec`.
 
 
 :mod:`importlib.abc` -- Abstract base classes related to import

Lib/importlib/__init__.py

@@ -164,6 +164,8 @@ def reload(module):
             pkgpath = None
         target = module
         spec = module.__spec__ = _bootstrap._find_spec(name, pkgpath, target)
+        if spec is None:
+            raise ModuleNotFoundError(f"spec not found for the module {name!r}", name=name)
         _bootstrap._exec(spec, module)
         # The module may have replaced itself in sys.modules!
         return sys.modules[name]

Lib/test/test_importlib/test_api.py

@@ -197,8 +197,6 @@ def find_module(name, path=None):
 
 class ReloadTests:
 
-    """Test module reloading for builtin and extension modules."""
-
     def test_reload_modules(self):
         for mod in ('tokenize', 'time', 'marshal'):
             with self.subTest(module=mod):
@@ -361,6 +359,18 @@ def test_reload_submodule(self):
             reloaded = self.init.reload(ham)
             self.assertIs(reloaded, ham)
 
+    def test_module_missing_spec(self):
+        #Test that reload() throws ModuleNotFounderror when reloading
+        # a module who's missing a spec. (bpo-29851)
+        name = 'spam'
+        with test_util.uncache(name):
+            module = sys.modules[name] = types.ModuleType(name)
+            # Sanity check by attempting an import.
+            module = self.init.import_module(name)
+            self.assertIsNone(module.__spec__)
+            with self.assertRaises(ModuleNotFoundError):
+                self.init.reload(module)
+
 
 (Frozen_ReloadTests,
  Source_ReloadTests

Misc/ACKS

@@ -774,6 +774,7 @@ Robert Kern
 Jim Kerr
 Magnus Kessler
 Lawrence Kesteloot
+Garvit Khatri
 Vivek Khera
 Dhiru Kholia
 Akshit Khurana

Misc/NEWS

@@ -604,6 +604,9 @@ Library
 - bpo-10379: locale.format_string now supports the 'monetary' keyword argument,
   and locale.format is deprecated.
 
+- bpo-29851: importlib.reload() now raises ModuleNotFoundError if the
+  module lacks a spec.
+
 - Issue #28556: Various updates to typing module: typing.Counter, typing.ChainMap,
   improved ABC caching, etc. Original PRs by Jelle Zijlstra, Ivan Levkivskyi,
   Manuel Krebber, and Łukasz Langa.