Counting depth or the deepest level a nested list

Question

A have a real problem (and a headache) with an assignment...

I'm in an introductory programming class, and I have to write a function that, given a list, will return the "maximum" depth it goes to... For example: [1,2,3] will return 1, [1,[2,3]] will return 2...

I've written this piece of code (it's the best I could get T_T)

def flat(l):
    count=0
    for item in l:
        if isinstance(item,list):
            count+= flat(item)
    return count+1

However, It obviously doens't work like it should, because if there are lists that do not count for the maximum deepness, it still raises the counter...

For example: when I use the function with [1,2,[3,4],5,[6],7] it should return 2, but it returns 3...

Any ideas or help would be greatly appreciated ^^ thanks a lot!! I've been strugling with this for weeks now...

Answer 1

Abusive way: Say your list is called mylist
mybrackets = map(lambda x: 1 if x=='[' else -1, [x for x in str(mylist) if x=='[' or x==']'])
maxdepth = max([sum(mybrackets[:i+1]) for i in range(len(mybrackets))])

This converts your list to a list of opening and closing brackets, then finds the largest number of opening brackets that occur before the corresponding closing bracket occurs.

Answer 2

Here is one way to write the function

depth = lambda L: isinstance(L, list) and max(map(depth, L))+1

I think the idea you are missing is to use max()

Answer 3

A way that does not need any additional modules and has the same speed, no mater what depth:

def depth(nested):
instring = False
count = 0
depthlist = []
for char in repr(nested):
    if char == '"' or char == "'":
        instring = not instring
    elif not instring and ( char == "[" or char == ")" ):
        count += 1
    elif not instring and ( char == "]" or char == ")" ):
        count -= 1
    depthlist.append(count)
return(max(depthlist))

Basically, what this does is convert the list to a string using repr(). Then for every character in this string equal to "(" or "[" it increases the variable count. for the closing brackets it decreases count. It then returns the maximum that counthas reached.

Answer 4

I extended the hammar's answer for every iterable (strings disabled by default):

def depth(arg, exclude=None):
    if exclude is None:
        exclude = (str, )

    if isinstance(arg, tuple(exclude)):
        return 0

    try:
        if next(iter(arg)) is arg:  # avoid infinite loops
            return 1
    except TypeError:
        return 0

    try:
        depths_in = map(lambda x: depth(x, exclude), arg.values())
    except AttributeError:
        try:
            depths_in = map(lambda x: depth(x, exclude), arg)
        except TypeError:
            return 0

    try:
        depth_in = max(depths_in)
    except ValueError:
        depth_in = 0

    return 1 + depth_in