bpo-42355: symtable.get_namespace() now checks whether there are multiple or any namespaces found (GH-23278)

Author: isidentical

Doc/library/symtable.rst

@@ -194,5 +194,5 @@ Examining Symbol Tables
 
    .. method:: get_namespace()
 
-      Return the namespace bound to this name.  If more than one namespace is
-      bound, :exc:`ValueError` is raised.
+      Return the namespace bound to this name. If more than one or no namespace
+      is bound to this name, a :exc:`ValueError` is raised.

Lib/symtable.py

@@ -306,11 +306,15 @@ def get_namespaces(self):
     def get_namespace(self):
         """Return the single namespace bound to this name.
 
-        Raises ValueError if the name is bound to multiple namespaces.
+        Raises ValueError if the name is bound to multiple namespaces
+        or no namespace.
         """
-        if len(self.__namespaces) != 1:
+        if len(self.__namespaces) == 0:
+            raise ValueError("name is not bound to any namespaces")
+        elif len(self.__namespaces) > 1:
             raise ValueError("name is bound to multiple namespaces")
-        return self.__namespaces[0]
+        else:
+            return self.__namespaces[0]
 
 if __name__ == "__main__":
     import os, sys

Lib/test/test_symtable.py

@@ -159,6 +159,10 @@ def test_namespaces(self):
         self.assertEqual(len(ns_test.get_namespaces()), 2)
         self.assertRaises(ValueError, ns_test.get_namespace)
 
+        ns_test_2 = self.top.lookup("glob")
+        self.assertEqual(len(ns_test_2.get_namespaces()), 0)
+        self.assertRaises(ValueError, ns_test_2.get_namespace)
+
     def test_assigned(self):
         self.assertTrue(self.spam.lookup("x").is_assigned())
         self.assertTrue(self.spam.lookup("bar").is_assigned())