Sum any nested level of iterables, with optional initial value

deep_add.py

from collections.abc import Iterable


def deep_add(*values, start=None):
    def _traverser(parts):
        for part in parts:
            if isinstance(part, Iterable):
                yield from _traverser(part)
            else:
                yield part
    ivalues = _traverser(values)
    if start is None:
        try:
            start = next(ivalues)
        except StopIteration:
            start = 0
    return sum(ivalues, start)