码迷,mamicode.com
首页 > 编程语言 > 详细

python Class:面向对象高级编程 __getitem__

时间:2018-07-20 13:58:11      阅读:155      评论:0      收藏:0      [点我收藏+]

标签:type   stop   ati   des   indexer   特定   round   dex   hid   

官网解释:

  • object.__getitem__(selfkey)

  • 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]

技术分享图片

print f[9]

技术分享图片

python Class:面向对象高级编程 __getitem__

标签:type   stop   ati   des   indexer   特定   round   dex   hid   

原文地址:http://blog.51cto.com/13502993/2147561

(0)
(0)
   
举报
评论 一句话评论(0
登录后才能评论!
© 2014 mamicode.com 版权所有  联系我们:gaon5@hotmail.com
迷上了代码!