def key2str(target):
    """
    In ``symfit`` there are many dicts with symbol: value pairs.
    These can not be used immediately as \*\*kwargs, even though this would make
    a lot of sense from the context.
    This function wraps such dict to make them usable as \*\*kwargs immediately.

    :param target: `Mapping` to be made save
    :return: `Mapping` of str(symbol): value pairs.
    """
    return target.__class__((str(symbol), value) for symbol, value in target.items())