Class Field

Lib/dataclasses.py:279–343

# When cls._FIELDS is filled in with a list of Field objects, the name
# and type fields will have been populated.
class Field:
    __slots__ = ('name',
                 'type',
                 'default',
                 'default_factory',
                 'repr',
                 'hash',
                 'init',
                 'compare',
                 'metadata',
                 'kw_only',
                 'doc',
                 '_field_type',  # Private: not to be used by user code.
                 )

    def __init__(self, default, default_factory, init, repr, hash, compare,
                 metadata, kw_only, doc):
        self.name = None
        self.type = None
        self.default = default
        self.default_factory = default_factory
        self.init = init
        self.repr = repr
        self.hash = hash
        self.compare = compare
        self.metadata = (_EMPTY_METADATA
                         if metadata is None else
                         types.MappingProxyType(metadata))
        self.kw_only = kw_only
        self.doc = doc
        self._field_type = None

    @recursive_repr()
    def __repr__(self):
        return ('Field('
                f'name={self.name!r},'
                f'type={self.type!r},'
                f'default={self.default!r},'
                f'default_factory={self.default_factory!r},'
                f'init={self.init!r},'
                f'repr={self.repr!r},'
                f'hash={self.hash!r},'
                f'compare={self.compare!r},'
                f'metadata={self.metadata!r},'
                f'kw_only={self.kw_only!r},'
                f'doc={self.doc!r},'
                f'_field_type={self._field_type}'
                ')')

    # This is used to support the PEP 487 __set_name__ protocol in the
    # case where we're using a field that contains a descriptor as a
    # default value.  For details on __set_name__, see
    # https://peps.python.org/pep-0487/#implementation-details.
    #
    # Note that in _process_class, this Field object is overwritten
    # with the default value, so the end result is a descriptor that
    # had __set_name__ called on it at the right time.
    def __set_name__(self, owner, name):