Issue #17098: Make sure every module has __loader__ defined.

Thanks to Thomas Heller for the bug report.

Lib/importlib/_bootstrap.py

@@ -1703,9 +1703,11 @@ def _setup(sys_module, _imp_module):
     else:
         BYTECODE_SUFFIXES = DEBUG_BYTECODE_SUFFIXES
 
-    for module in (_imp, sys):
-        if not hasattr(module, '__loader__'):
-            module.__loader__ = BuiltinImporter
+    module_type = type(sys)
+    for module in sys.modules.values():
+        if isinstance(module, module_type):
+            if not hasattr(module, '__loader__'):
+                module.__loader__ = BuiltinImporter
 
     self_module = sys.modules[__name__]
     for builtin_name in ('_io', '_warnings', 'builtins', 'marshal'):

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 3.3.1?
 Core and Builtins
 -----------------
 
+- Issue #17098: All modules now have __loader__ set even if they pre-exist the
+  bootstrapping of importlib.
+
 - Issue #16979: Fix error handling bugs in the unicode-escape-decode decoder.
 
 - Issue #13886: Fix input() to not strip out input bytes that cannot be decoded

Modules/signalmodule.c

@@ -1367,9 +1367,8 @@ PyErr_SetInterrupt(void)
 void
 PyOS_InitInterrupts(void)
 {
-    PyObject *m = PyInit_signal();
+    PyObject *m = PyImport_ImportModule("signal");
     if (m) {
-        _PyImport_FixupBuiltin(m, "signal");
         Py_DECREF(m);
     }
 }