class MyRecord(Record): v = one_of('a', 'b', 'c', coerce=text_type.lower)
class MyRecord(Record): v = one_of('a', 'b', 'c', nullable=True)
class MyRecord(Record): v = one_of('a', 'b', 'c', nullable=True, default='z')
class MyRecord(Record): v = nullable(one_of('a', 'b', 'c'))
class MyRecord(Record): c = one_of(c1)
def _(): with assert_raises(ValueError): one_of('a', object())
def _(): with assert_raises(ValueError): one_of()
class MyRecord(Record): v = one_of('a', 'b', 'c')