code: def test_return_py(self):
      class X(A):
          def f(self):
              return "X.f"
  
      x = X()
  
      self.assertEqual("X.f", x.f())
      self.assertEqual("X.f", call_f(x))
  
file_path: turicreate/src/external/boost/boost_1_68_0/libs/python/test/polymorphism2.py
imports: import unittest
  import sys
label_desc: Use image node_id 4 for calling the PolymorphTest obj's underlying member method code with example usage: obj.test_return_py() and returns: str