How to convert nested list into a single list in python?
You are getting the error because of string value contains in the nested list.
You need to handle string value as well.

You can fix the error by following codes:

from collections import Iterable

def single_list(list,ignore_types=(str)): 
for item in list:
    if isinstance(item, Iterable) and not isinstance(item, ignore_types):
        yield from single_list(item,ignore_types=(str))
    else:
        yield item

Item_list = [10,20,[30,40],[50,'Null',70],100]
items_single=single_list(Item_list)
for item in items_single:
    print(item)