Remove sys.last_traceback attribute using del instead of setting to None

AUTHORS

@@ -165,6 +165,7 @@ Marcelo Duarte Trevisani
 Marcin Bachry
 Marco Gorelli
 Mark Abramowitz
+Mark Dickinson
 Markus Unterwaditzer
 Martijn Faassen
 Martin Altmayer

changelog/6255.bugfix.rst

@@ -0,0 +1,3 @@
+Clear the ``sys.last_traceback``, ``sys.last_type`` and ``sys.last_value``
+attributes by deleting them instead of setting them to ``None``. This better
+matches the behaviour of the Python standard library.

src/_pytest/runner.py

@@ -121,7 +121,12 @@ def pytest_runtest_setup(item):
 
 def pytest_runtest_call(item):
     _update_current_test_var(item, "call")
-    sys.last_type, sys.last_value, sys.last_traceback = (None, None, None)
+    try:
+        del sys.last_type
+        del sys.last_value
+        del sys.last_traceback
+    except AttributeError:
+        pass
     try:
         item.runtest()
     except Exception:

testing/test_runner.py

@@ -900,9 +900,9 @@ def runtest(self):
     # The next run should clear the exception info stored by the previous run
     ItemMightRaise.raise_error = False
     runner.pytest_runtest_call(ItemMightRaise())
-    assert sys.last_type is None
-    assert sys.last_value is None
-    assert sys.last_traceback is None
+    assert not hasattr(sys, "last_type")
+    assert not hasattr(sys, "last_value")
+    assert not hasattr(sys, "last_traceback")
 
 
 def test_current_test_env_var(testdir, monkeypatch):