old_contents: 'test abstract classes'
  
  __pychecker__ = 'no-classdoc'
  
  class Abstract:
      def f(self): raise SystemError("override in subclass")
      def g(self): raise KeyError("override in subclass")
  class ConcreteBad(Abstract):
      def g(self): pass
  class ConcreteGood(ConcreteBad):
      def f(self): pass
  a = Abstract()                          # error
  cb = ConcreteBad()                      # error
  cg = ConcreteGood()                     # ok, f defined
  
  cb.g()
  def f():
      class MoreBad(Abstract):
          def g(): pass
      _ = MoreBad()                       # FIXME, error not caught
  
  import import73
  class ImplAbstract(import73.AbstractLib):
      def __init__(self):
          import73.AbstractLib.__init__(self)
  
  def lib_example():
      _ = import73.AbstractLib()          # error
      _ = ImplAbstract()                  # error
  
new_contents: 'test abstract classes'
  
  __pychecker__ = 'no-classdoc'
  
  class Abstract:
      def f(self): raise SystemError("override in subclass")
      def g(self): raise KeyError("override in subclass")
  class ConcreteBad(Abstract):
      def g(self): pass
  class ConcreteGood(ConcreteBad):
      def f(self): pass
  a = Abstract()                          # error
  cb = ConcreteBad()                      # error
  cg = ConcreteGood()                     # ok, f defined
  
  cb.g()
  def f():
      class MoreBad(Abstract):
          def g(): pass
      _ = MoreBad()                       # FIXME, error not caught
  
  import import73
  class ImplAbstract(import73.AbstractLib):
      def __init__(self):
          import73.AbstractLib.__init__(self)
  
  def lib_example():
      _ = import73.AbstractLib()          # error
      unused = ImplAbstract()             # error
  
subject: use a diff var to avoid inconsistent var use warning