Helper to create bytes values. (Derived from string generator)

def _bytes_generator(descriptor, max_length=0, limit=0):
    'Helper to create bytes values. (Derived from string generator)'
    strs = values.get_strings(max_length, limit)
    vals = [bytes(_, 'utf-8') for _ in strs]
    return gen.IterValueGenerator(descriptor.name, vals)