def METHOD_NAME(self, env):
    """Processes a package, creating a new
    :class:`~oioioi.problems.models.Problem` or updating an existing
    one.
    This function will be called either from
    :func:`~oioioi.problems.unpackmgr.unpackmgr_job` (Celery task)
    or from :func:`~oioioi.problems.package.simple_unpack` (e.g. when
    a problem is added from a command line).
    Used ``env`` keys:
      ``package_id``: an id of the
      :class:`~oioioi.problems.models.ProblemPackage` instance
      with the package file to unpack.
    Produced ``env`` keys:
      ``problem_id``: an id of the
      :class:`~oioioi.problems.models.Problem` instance
      representing the created or modified problem.
    """
    raise NotImplementedError