<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_formatter(name):
 """Return the named formatter function. See the function "set_formatter" for details. """

    if name in ('self', 'instance', 'this'):
        return af_self
    elif name == 'class':
        return af_class
    elif name in ('named', 'param', 'parameter'):
        return af_named
    elif name in ('default', 'optional'):
        return af_default
#    elif name in ('anonymous', 'arbitrary', 'unnamed'):
#        return af_anonymous
    elif name in ('keyword', 'pair', 'pairs'):
        return af_keyword
    else:
        raise ValueError('unknown trace formatter %r' % name)