Python 3.5，斐波数列， a,b = 0,1

Question

class Fib(object):

def __getitem__(self, n):
    a, b = 0, 1
    for x in range(n):
        a, b = b, a + b
    return a
    

f = Fib()
f[0] = 0

不解为什么是f[0] = 0

函数是不是直接执行Return 再回到循环体？

初学者还有很多不懂，请多指教，谢谢

Answer 1

Using the subscript value operator []的时候，程序会去访问对象的__getitem__ function.

f[0] 相当于 f.__getitem__(self, 0) ，nAssigned value is 0

a = 0, b = 1
for x in range(0):   # 这里range(0) 直接跳过
    a, b = b, a + b
return a             # a = 0

Sof[0] = 0.

I don’t know what’s going on, so I debug it step by step and check the documentation.

Answer 2

If

f[0], that is n = 0

for x in range(n):
    a, b = b, a + b

The loop body returns directly, so a has not changed and is still 0.