flatten.py

from collections import Iterable, Mapping
from operator import methodcaller

def flatten(it, map_iter='values', max_depth=128):
    if max_depth < 0:
        try:
            raise RecursionError('maximum recursion depth exceded in flatten')
        except NameError:
            raise Exception('maximum recursion depth exceded in flatten')
    elif isinstance(it, str):
        yield it
    elif isinstance(it, Mapping):
        for item in methodcaller(map_iter)(it):
            for x in flatten(
                    item, map_iter=map_iter, max_depth=max_depth-1):
                yield x
    elif isinstance(it, Iterable):
        for item in it:
            yield x
    else:
        yield it