old_contents: #: Okay
  class ActionError(Exception):
      pass
  #: N818
  class ActionClass(Exception):
      pass
  #: Okay
  class ActionError(Exception):
      pass
  class DeepActionError(ActionError):
      pass
  #: N818
  class ActionError(Exception):
      pass
  class DeepActionClass(ActionError):
      pass
  #: Okay
  class MixinError(Exception):
      pass
  class Mixin:
      pass
  class MixinActionError(Mixin,MixinError):
      pass
  #: N818
  class MixinError(Exception):
      pass
  class Mixin:
      pass
  class MixinActionClass(Mixin,MixinError):
      pass
  
new_contents: #: Okay
  class ActionError(Exception):
      pass
  #: N818
  class ActionClass(Exception):
      pass
  #: Okay
  class ActionError(Exception):
      pass
  class DeepActionError(ActionError):
      pass
  #: N818
  class ActionError(Exception):
      pass
  class DeepActionClass(ActionError):
      pass
  #: Okay
  class MixinError(Exception):
      pass
  class Mixin:
      pass
  class MixinActionError(Mixin, MixinError):
      pass
  #: N818
  class MixinError(Exception):
      pass
  class Mixin:
      pass
  class MixinActionClass(Mixin, MixinError):
      pass
  
subject: Add spaces after commas.