<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def config(client, key, value):
 """Get and set Renku repository and global options."""

    if value is None:
        cfg = client.repo.config_reader()
        click.echo(cfg.get_value(*_split_section_and_key(key)))
    else:
        with client.repo.config_writer() as cfg:
            section, config_key = _split_section_and_key(key)
            cfg.set_value(section, config_key, value)
            click.echo(value)