<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _tag_type_to_explicit_implicit(params):
 """ Converts old-style "tag_type" and "tag" params to "explicit" and "implicit" :param params: A dict of parameters to convert from tag_type/tag to explicit/implicit """


    if 'tag_type' in params:
        if params['tag_type'] == 'explicit':
            params['explicit'] = (params.get('class', 2), params['tag'])
        elif params['tag_type'] == 'implicit':
            params['implicit'] = (params.get('class', 2), params['tag'])
        del params['tag_type']
        del params['tag']
        if 'class' in params:
            del params['class']