<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def data_spec(cls, name):
 """ Return the fileset_spec, i.e. the template of the fileset expected to be supplied or generated corresponding to the fileset_spec name. Parameters name : Str Name of the fileset_spec to return """

        # If the provided "name" is actually a data item or parameter then
        # replace it with its name.
        if isinstance(name, BaseData):
            name = name.name
        try:
            return cls._data_specs[name]
        except KeyError:
            raise ArcanaNameError(
                name,
                "No fileset spec named '{}' in {}, available:\n{}"
                .format(name, cls.__name__,
                        "\n".join(list(cls._data_specs.keys()))))