def f(arr):
    return 0 if not arr else arr[0] + f(arr[1:])
print(f([]))

def f(arr):
    return arr[0] if len(arr) == 1 else arr[0] + f(arr[1:])
print(f([]))

def f(arr):
    first, *rest = arr
    return first if not rest else first + f(rest)
print(f([]))

def f(n):
    def g(x):
        return x**n
    return g
g = f(2)
print(g(7))

def f():
    _x = None
    def g(x=None):
        nonlocal _x
        if x is None:
            return _x
        _x = x
    return g
g = f()
print(g(), g(10), g(), g(5), g())

def f(x):
    y = x ** 2
    return y
print(*f.__code__.co_varnames)

def f(x, y):
    f.y = y
    f.z = f.y
    return x
print(f(1, 2), [x for x in dir(f) if not x.startswith('__')])

def f(arr):
    return 0 if not arr else arr[0] + f(arr[1:])
print(f(('a', 'b', 'c', 'd')))

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')))