docs: def deprecated(instructions):
      """
      Flags a method as deprecated.
  
      :param instructions: A human-friendly string of instructions, such as: 'Please migrate to add_proxy() ASAP.'
      :return: DeprecatedWarning
      """
      def decorator(func):
          """This is a decorator which can be used to mark functions as deprecated.
  
          It will result in a warning being emitted when the function is used.
          """
          @functools.wraps(func)
          def wrapper(*args, **kwargs):
              message = 'Call to deprecated function {}. {}'.format(func.__name__,
                                                                    instructions)
              frame = inspect.currentframe().f_back
              warnings.warn_explicit(message,
                                     category=DeprecatedWarning,
                                     filename=inspect.getfile(frame.f_code),
                                     lineno=frame.f_lineno)
              return func(*args, **kwargs)
          return wrapper
      return decorator