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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def filter_genes_only(stmts_in, **kwargs):
 """Filter to statements containing genes only. Parameters stmts_in : list[indra.statements.Statement] A list of statements to filter. specific_only : Optional[bool] If True, only elementary genes/proteins will be kept and families will be filtered out. If False, families are also included in the output. Default: False save : Optional[str] The name of a pickle file to save the results (stmts_out) into. remove_bound: Optional[bool] If true, removes bound conditions that are not genes If false (default), filters out statements with non-gene bound conditions Returns ------- stmts_out : list[indra.statements.Statement] A list of filtered statements. """

    remove_bound = 'remove_bound' in kwargs and kwargs['remove_bound']

    specific_only = kwargs.get('specific_only')
    logger.info('Filtering %d statements for ones containing genes only...' % 
                len(stmts_in))
    stmts_out = []
    for st in stmts_in:
        genes_only = True
        for agent in st.agent_list():
            if agent is not None:
                criterion = lambda a: _agent_is_gene(a, specific_only)
                if not criterion(agent):
                    genes_only = False
                    break
                if remove_bound:
                    _remove_bound_conditions(agent, criterion)
                else:
                    if _any_bound_condition_fails_criterion(agent, criterion):
                        genes_only = False
                        break

        if genes_only:
            stmts_out.append(st)
    logger.info('%d statements after filter...' % len(stmts_out))
    dump_pkl = kwargs.get('save')
    if dump_pkl:
        dump_statements(stmts_out, dump_pkl)
    return stmts_out