remove the legacy code about im_func and generalize using fix and compat.getimfunc

src/_pytest/python.py

@@ -37,6 +37,7 @@ from _pytest.compat import (
     getlocation,
     enum,
     get_default_arg_names,
+    getimfunc,
 )
 from _pytest.outcomes import fail
 from _pytest.mark.structures import (
@@ -681,14 +682,12 @@ class Class(PyCollector):
     def setup(self):
         setup_class = _get_xunit_func(self.obj, "setup_class")
         if setup_class is not None:
-            setup_class = getattr(setup_class, "im_func", setup_class)
-            setup_class = getattr(setup_class, "__func__", setup_class)
+            setup_class = getimfunc(setup_class)
             setup_class(self.obj)
 
         fin_class = getattr(self.obj, "teardown_class", None)
         if fin_class is not None:
-            fin_class = getattr(fin_class, "im_func", fin_class)
-            fin_class = getattr(fin_class, "__func__", fin_class)
+            fin_class = getimfunc(fin_class)
             self.addfinalizer(lambda: fin_class(self.obj))
 
 
@@ -1433,7 +1432,7 @@ class Function(FunctionMixin, nodes.Item, fixtures.FuncargnamesCompatAttr):
     @property
     def function(self):
         "underlying python 'function' object"
-        return getattr(self.obj, "im_func", self.obj)
+        return getimfunc(self.obj)
 
     def _getobj(self):
         name = self.name

src/_pytest/unittest.py

@@ -9,6 +9,7 @@ import _pytest._code
 from _pytest.config import hookimpl
 from _pytest.outcomes import fail, skip, xfail
 from _pytest.python import transfer_markers, Class, Module, Function
+from _pytest.compat import getimfunc
 
 
 def pytest_pycollect_makeitem(collector, name, obj):
@@ -53,7 +54,7 @@ class UnitTestCase(Class):
             x = getattr(self.obj, name)
             if not getattr(x, "__test__", True):
                 continue
-            funcobj = getattr(x, "im_func", x)
+            funcobj = getimfunc(x)
             transfer_markers(funcobj, cls, module)
             yield TestCaseFunction(name, parent=self, callobj=funcobj)
             foundsomething = True

testing/python/metafunc.py

@@ -796,7 +796,7 @@ class TestMetafuncFunctional(object):
         p = testdir.makepyfile(
             """
             # assumes that generate/provide runs in the same process
-            import sys, pytest
+            import sys, pytest, six
             def pytest_generate_tests(metafunc):
                 metafunc.addcall(param=metafunc)
 
@@ -815,11 +815,7 @@ class TestMetafuncFunctional(object):
                 def test_method(self, metafunc, pytestconfig):
                     assert metafunc.config == pytestconfig
                     assert metafunc.module.__name__ == __name__
-                    if sys.version_info > (3, 0):
-                        unbound = TestClass.test_method
-                    else:
-                        unbound = TestClass.test_method.im_func
-                    # XXX actually have an unbound test function here?
+                    unbound = six.get_unbound_function(TestClass.test_method)
                     assert metafunc.function == unbound
                     assert metafunc.cls == TestClass
         """