code: def validate(self, value):
          
          value = super(Ascii, self).validate(value)
          if value:
              charset = value if isinstance(
                  value, (bytearray, )) else map(ord, value)
              if not set(range(128)).issuperset(charset):
                  raise ValidationError(
                      '{!r} is not an ASCII string.'.format(value))
          return value
docs: Only allow ASCII and None values.
  
          Check against US-ASCII, a.k.a. 7-bit ASCII, a.k.a. ISO646-US, a.k.a.
          the Basic Latin block of the Unicode character set.
  
          Source: https://github.com/apache/cassandra/blob
          /3dcbe90e02440e6ee534f643c7603d50ca08482b/src/java/org/apache/cassandra
          /serializers/AsciiSerializer.java#L29