def merge_sequentials_containing_ints(*args):
    """takes a bunch of sequential data (of the same type and structured as
    <key,value>) and merges them together by adding (not concatenating) their
    values. data should be structured homogeneously.
    WARNING: duplicate items within an argument are also merged. strings not
    allowed."""
    if not len(args):
        return ()
    if isinstance(args[0], str):
        raise ValueError("Strings are't allowed.")
    res = {}
    for arg in args:
        for key, val in arg:
            res[key] = val + res.get(key, 0)
    return tuple(res.items())
