code: def DateField(formatter=types.DEFAULT_DATE_FORMAT, default=NOTHING,
                required=True, repr=True, cmp=True, key=None):
      
      default = _init_fields.init_default(required, default, None)
      validator = _init_fields.init_validator(required, date)
      converter = converters.to_date_field(formatter)
      return attrib(default=default, converter=converter, validator=validator,
                    repr=repr, cmp=cmp,
                    metadata=dict(formatter=formatter, key=key))
docs: Create new date field on a model.
  
      :param formatter: date formatter string (default: "%Y-%m-%d")
      :param default: any date or string that can be converted to a date value
      :param bool required: whether or not the object is invalid if not provided.
      :param bool repr: include this field should appear in object's repr.
      :param bool cmp: include this field in generated comparison.
      :param string key: override name of the value when converted to dict.