Flattened List (Python recipe) by marlonamor

ActiveState Code (http://code.activestate.com/recipes/576719/)

The best I've been able to come up with thus far is:

def deep_flatten(iter_):
    if hasattr(iter_, '__iter__') or hasattr(iter, '__getitem__'):
        for item in iter_:
            for elem in deep_flatten(item):
                yield elem
    else:
        yield iter_

The "best" solution would seem to me to be:

def deep_flatten2(iter_):
    try:
        for item in iter_:
            for elem in deep_flatten2(item):
                yield elem
    except TypeError:
        yield iter_

but I keep getting the following warnings:

Exception RuntimeError: 'maximum recursion depth exceeded while calling a Python object' in <type 'exceptions.TypeError'> ignored

Anyone know why I get that error? Even with just 2 "levels" of flattening to do, I hit a recursion depth error, which seems incorrect.

@Matthew Wood:

For the same reason that the str special case is in the recipe. Iterating a string produces strings of length 1. Since 'o' is an iterable of length 1, deep_flatten('o') will keep stepping into the try clause without ever generating a TypeError.

-1 for not working in the general case.

By checking types, you limit yourself to a finite number of classes that will "work" here. Without using ABCs (which won't always work) you have to limit yourself to either a finite number of stringlike objects, or a finite number of non-stringlike iterables.

You know what works waaay better than this recipe? Not being in a situation where you have to flatten arbitrarily-nested iterables in the first place. It's less common and more easily-avoidable than you think, and then you don't get into awful situations like this.

Good points so we can recall the solution from Matthew with a small modification:

def deepFlatten(lista): try: for item in lista: for one in deepFlatten(item): yield one except: yield lista

Just remove the exception object 'TypeError'