def f(arr):
    return arr[0] if len(arr) == 1 else arr[0] + f(arr[1:])
print(f(('a', 'b', 'c', 'd')))

def f(arr):
    first, *rest = arr
    return first if not rest else first + f(rest)
print(f(('H', 'e', 'l', 'l', 'o')))

def f(a: int, b: float) -> int:
         return a * int(b) 
print(f(5, 2.1))

def func(a: str, b: int):
    return a + b 
func(1, 2)
for arg in sorted(func.__annotations__):
    print(arg, func.__annotations__[arg])
    break

def f(x, y):
    z = x ** y
    return z
print(f.__code__.co_argcount)

def f(arr):
    s = 0
    for x in arr:
        if not isinstance(x, list):
            s += x
        else:
            s += f(x)
    return s
print(f([1, [2, [3, [4, [5]]]]]))

from collections.abc import Iterable
def f(arr):
    s = 0
    items = list(arr)
    while items:
        first = items.pop(0)
        if not isinstance(first, Iterable):
            s += first
        else:
            items.extend(first)
    return s
print(f((1, (2, (3, (4, (5)))))))

def f(L):
    s = ''
    items = list(L)
    while items:
        first = items.pop(0)
        if isinstance(first, str):
            s += first
        else:
            items[:0] = first       
    return s
print(f(('a', ('b', ('c', ('d', 'e'))))))

def f(a: int = 2, b: int = 2) -> int:
    return a ** b
print(f(3))

def f(a: int = 2, b: int = 2) -> int:
    return a ** b
print(f(3))