nose: type annotate with some resulting refactoring

src/_pytest/nose.py

@@ -1,33 +1,35 @@
 """Run testsuites written for nose."""
-from _pytest import python
-from _pytest import unittest
 from _pytest.config import hookimpl
 from _pytest.fixtures import getfixturemarker
 from _pytest.nodes import Item
+from _pytest.python import Function
+from _pytest.unittest import TestCaseFunction
 
 
 @hookimpl(trylast=True)
-def pytest_runtest_setup(item) -> None:
-    if is_potential_nosetest(item):
-        if not call_optional(item.obj, "setup"):
-            # Call module level setup if there is no object level one.
-            call_optional(item.parent.obj, "setup")
-        # XXX This implies we only call teardown when setup worked.
-        item.addfinalizer(lambda: teardown_nose(item))
+def pytest_runtest_setup(item: Item) -> None:
+    if not isinstance(item, Function):
+        return
+    # Don't do nose style setup/teardown on direct unittest style classes.
+    if isinstance(item, TestCaseFunction):
+        return
 
+    # Capture the narrowed type of item for the teardown closure,
+    # see https://github.com/python/mypy/issues/2608
+    func = item
 
-def teardown_nose(item) -> None:
-    if is_potential_nosetest(item):
-        if not call_optional(item.obj, "teardown"):
-            call_optional(item.parent.obj, "teardown")
+    if not call_optional(func.obj, "setup"):
+        # Call module level setup if there is no object level one.
+        assert func.parent is not None
+        call_optional(func.parent.obj, "setup")  # type: ignore[attr-defined]
 
+    def teardown_nose() -> None:
+        if not call_optional(func.obj, "teardown"):
+            assert func.parent is not None
+            call_optional(func.parent.obj, "teardown")  # type: ignore[attr-defined]
 
-def is_potential_nosetest(item: Item) -> bool:
-    # Extra check needed since we do not do nose style setup/teardown
-    # on direct unittest style classes.
-    return isinstance(item, python.Function) and not isinstance(
-        item, unittest.TestCaseFunction
-    )
+    # XXX This implies we only call teardown when setup worked.
+    func.addfinalizer(teardown_nose)
 
 
 def call_optional(obj: object, name: str) -> bool: