import typing


def dict_merge(
    dict_a: typing.Dict[typing.Any, typing.Any],
    dict_b: typing.Mapping[typing.Any, typing.Any],
) -> typing.Dict[typing.Any, typing.Any]:
    """Merge items from dict_b into dict_a, not overriding existing keys.

    This is effectively the same as the merge operator in python 3.9: dict_a | dict_b
    """
    dict_a.update({key: value for key, value in dict_b.items() if key not in dict_a})
    return dict_a