Function _init_fn

Lib/dataclasses.py:670–725

(fields, std_fields, kw_only_fields, frozen, has_post_init,
             self_name, func_builder, slots)

def _init_fn(fields, std_fields, kw_only_fields, frozen, has_post_init,
             self_name, func_builder, slots):
    # fields contains both real fields and InitVar pseudo-fields.

    # Make sure we don't have fields without defaults following fields
    # with defaults.  This actually would be caught when exec-ing the
    # function source code, but catching it here gives a better error
    # message, and future-proofs us in case we build up the function
    # using ast.

    seen_default = None
    for f in std_fields:
        # Only consider the non-kw-only fields in the __init__ call.
        if f.init:
            if not (f.default is MISSING and f.default_factory is MISSING):
                seen_default = f
            elif seen_default:
                raise TypeError(f'non-default argument {f.name!r} '
                                f'follows default argument {seen_default.name!r}')

    annotation_fields = [f.name for f in fields if f.init]

    locals = {'__dataclass_HAS_DEFAULT_FACTORY__': _HAS_DEFAULT_FACTORY,
              '__dataclass_builtins_object__': object}

    body_lines = []
    for f in fields:
        line = _field_init(f, frozen, locals, self_name, slots)
        # line is None means that this field doesn't require
        # initialization (it's a pseudo-field).  Just skip it.
        if line:
            body_lines.append(line)

    # Does this class have a post-init function?
    if has_post_init:
        params_str = ','.join(f.name for f in fields
                              if f._field_type is _FIELD_INITVAR)
        body_lines.append(f'  {self_name}.{_POST_INIT_NAME}({params_str})')

    # If no body lines, use 'pass'.
    if not body_lines:
        body_lines = ['  pass']

    _init_params = [_init_param(f) for f in std_fields]
    if kw_only_fields:
        # Add the keyword-only args.  Because the * can only be added if
        # there's at least one keyword-only arg, there needs to be a test here
        # (instead of just concatenating the lists together).
        _init_params += ['*']
        _init_params += [_init_param(f) for f in kw_only_fields]
    func_builder.add_fn('__init__',
                        [self_name] + _init_params,
                        body_lines,
                        locals=locals,
                        return_type=None,
                        annotation_fields=annotation_fields)