pythongh-87115: Set __main__.__spec__ to None in pdb (python#116141)

Author: gaogaotiantian

Lib/pdb.py

@@ -188,6 +188,7 @@ def namespace(self):
             __name__='__main__',
             __file__=self,
             __builtins__=__builtins__,
+            __spec__=None,
         )
 
     @property

Lib/test/test_pdb.py

@@ -2695,6 +2695,18 @@ def bœr():
             ('bœr', 2),
         )
 
+    def test_spec(self):
+        # Test that __main__.__spec__ is set to None when running a script
+        script = """
+            import __main__
+            print(__main__.__spec__)
+        """
+
+        commands = "continue"
+
+        stdout, _ = self.run_pdb_script(script, commands)
+        self.assertIn('None', stdout)
+
     def test_find_function_first_executable_line(self):
         code = textwrap.dedent("""\
             def foo(): pass

Misc/NEWS.d/next/Library/2024-02-29-20-06-06.gh-issue-87115.FVMiOR.rst

@@ -0,0 +1 @@
+Set ``__main__.__spec__`` to ``None`` when running a script with :mod:`pdb`