extract_words

def extract_words(mixture):
    """
    Flat deep nested iterables and split strings if they occour.
    """
    stack = deque([mixture])
    # using a stack to allow iterating
    # deep nested list
    # it could be done easier with recursion
    # but all stack based languages have a recursion limit
    to_split = (str, bytes)
    # we want to split str and bytes
    while stack:
        # loop runs until stack is empty
        current = stack.popleft()
        # with the first iteration
        # stack is currently empty
        # and current has the first element from stack
        if isinstance(current, to_split):
            # split if the current object is a str or bytes
            yield from current.split()
        else:
            # this branch is executed, if the current object
            # is not a str or bytes
            try:
                current = iter(current)
                # iter of iter returns the same iterator
                subelement = next(current)
                # the next does what the for loop does
            except StopIteration:
                # but we have to check for errors manually
                pass
            except TypeError:
                # and if an element is not iterable, it raieses
                # TypeError. Intgers are for example are not
                # iterable
                yield subelement
            else:
                # if no error happens, put the current iterator back
                # to the left side of the stack
                stack.appendleft(current)
                # put the subelement of the beginning of the deque
                stack.appendleft(subelement)


data = ['Test eins zwei drei', ['hallo', '123'], [[[[['foo bar']]], 'bat']], 12]
extractor = extract_words(data)

result = list(extractor)
print(result)