make sure doctest doesn't pollute __builtins__

This was causing test_builtin to fail after the decimal doctests were run
see #3462

diff --git a/Lib/doctest.py b/Lib/doctest.py
index 476c718f023cb16273ec29baa7a37533380e8b29..64a0375da31e2b4c68b9f49bc633a252c493c662 100644 (file)
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -1360,6 +1360,7 @@ class DocTestRunner:
             linecache.getlines = self.save_linecache_getlines
             if clear_globs:
                 test.globs.clear()
+                __builtins__['_'] = None
 
     #/////////////////////////////////////////////////////////////////
     # Summarization