from functools import reduce

'''
flatten function takes one input parameter which may contains hierarchical list of integers and flatten to single dimesnion List.

First parameter of lambda function calls same function recursively if first element of array is list type
([a],flatten(a))[type(a) ==list]

Second parameter of lambda function calls same function recursively if second element of array is list type
([b],flatten(b))[type(b) ==list]

reduce function keep pulls the elements in array tills end and append to array

last part of code executes for least granular element
if  type(y) ==list and len(y)>1 else y

'''
def flatten(y):
    return reduce(lambda a,b:([a],flatten(a))[type(a) ==list] +([b],flatten(b))[type(b) ==list],y)  \
    if  type(y) ==list and len(y)>1 else y



if __name__ == '__main__':
    try:
       l_arr_in = [1, [2, 3], [4, 5, 6], [7], [[8, 9], 9], 10, [20, 30, [40, [50, [60, [70, 80]]]]]]
       print(flatten(l_arr_in))
    except IndexError as e:
        print ("Error :--", e)
    except Exception as e:
        print ("Error :--", e)