Python Set of All Element in a Nested List

Question

I’m trying to have all element in a nested list return in the form of set through this function, but errors occurred.

list = [[0,4], [2,4], 5, [[[7,2], 3], 4]]

def setof(list):
  bag = set()
  for item in list:
    try: bag.add(item)
    except TypeError: bag.add(setof(item))
  return bag

print(setof(list))

Errors:
try: bag.add(item)
TypeError: unhashable type: ‘list’
During handling of the above exception, another exception occurred:
print(setof(list))
except TypeError: bag.add(setof(item))
TypeError: unhashable the: ‘set’

Does anyone know why did this happen or how to fix it, or a better way of doing it? This is my first time here. Thanks!

From [this question](https://stackoverflow.com/questions/10823877/what-is-the-fastest-way-to-flatten-arbitrarily-nested-lists-in-python) you could just call `set(flatten(data))` and that would work — Cory Kramer, Apr 24 '20 at 15:54
It would pay to put your code, error, and expected output in separate code blocks. More information on [crafting questions can be found here](https://stackoverflow.com/help/how-to-ask) — Adrian Torrie, Apr 24 '20 at 16:57

score 0 · Accepted Answer · answered Apr 24 '20 at 15:53

0

bag.add(setof(item)) is trying to add a set as an element of bag, not combine the sets. Use

bag.update(setof(item))

answered Apr 24 '20 at 15:53

Barmar

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score 0 · Answer 2 · answered Apr 24 '20 at 15:55

Your problem is coming from set.add(list). This is not something Python sets accept. So, you want to turn all the inner lists into sets. Try this:

def setof(lst):
    bag = set()
    for item in lst:
        try:
            bag.add(set(item))
        except TypeError:
            bag.add(set([item]))
    return bag

Python Set of All Element in a Nested List

2 Answers2