python Class：面向对象高级编程 __getitem__

官网解释:

object.

__getitem__

(self, key)

Called to implement evaluation of

self[key]

. For sequence types, the accepted keys should be integers and slice objects. Note that the special interpretation of negative indexes (if the class wishes to emulate a sequence type) is up to the

__getitem__()

method. If key is of an inappropriate type,

TypeError

may be raised; if of a value outside the set of indexes for the sequence (after any special interpretation of negative values),

IndexError

should be raised. For mapping types, if key is missing (not in the container),

KeyError

should be raised.Note:

for

loops expect that an

IndexError

will be raised for illegal indexes to allow proper detection of the end of the sequence.

对于Fibonacci数列，当我们想抽取特定位置的值看，那又该怎么做，于是就出来了__getitem__这样的函数。

int、list类型：切片(没有step)

#!/usr/bin/python
# -*- coding: utf-8 -*-

class Fib(object):
def __getitem__(self, n):
if isinstance(n, int): # n是索引
a, b = 1, 1
for x in range(n):
a, b = b, a + b
return a
if isinstance(n, slice): # n是切片
start = n.start
stop = n.stop
if start is None:
start = 0
a, b = 1, 1
L = []
for x in range(stop):
if x >= start:
L.append(a)
a, b = b, a + b
return L

f = Fib()
print f[0:4]



print f[9]