Function evolve

src/attr/_make.py:587–642

Create a new instance, based on the first positional argument with *changes* applied. .. tip:: On Python 3.13 and later, you can also use `copy.replace` instead. Args: inst: Instance of a class with *attrs* attributes. *inst* must be passed

(*args, **changes)

def evolve(*args, **changes):
    """
    Create a new instance, based on the first positional argument with
    *changes* applied.

    .. tip::

       On Python 3.13 and later, you can also use `copy.replace` instead.

    Args:

        inst:
            Instance of a class with *attrs* attributes. *inst* must be passed
            as a positional argument.

        changes:
            Keyword changes in the new copy.

    Returns:
        A copy of inst with *changes* incorporated.

    Raises:
        TypeError:
            If *attr_name* couldn't be found in the class ``__init__``.

        attrs.exceptions.NotAnAttrsClassError:
            If *cls* is not an *attrs* class.

    .. versionadded:: 17.1.0
    .. deprecated:: 23.1.0
       It is now deprecated to pass the instance using the keyword argument
       *inst*. It will raise a warning until at least April 2024, after which
       it will become an error. Always pass the instance as a positional
       argument.
    .. versionchanged:: 24.1.0
       *inst* can't be passed as a keyword argument anymore.
    """
    try:
        (inst,) = args
    except ValueError:
        msg = (
            f"evolve() takes 1 positional argument, but {len(args)} were given"
        )
        raise TypeError(msg) from None

    cls = inst.__class__
    attrs = fields(cls)
    for a in attrs:
        if not a.init:
            continue
        attr_name = a.name  # To deal with private attributes.
        init_name = a.alias
        if init_name not in changes:
            changes[init_name] = getattr(inst, attr_name)

    return cls(**changes)