一个Python3和Python2的range差异
一个Python3和Python2的range差异
用户1416054
发布于 2018-08-02 12:03:50
发布于 2018-08-02 12:03:50
文章被收录于专栏：JackeyGao的博客
一个Python3和Python2的range差异
Posted December 20, 2017
Python 3 中执行100000000 in range(100000001)会比Python 2快的非常多。
Bash
$ time python -c "100000000 in range(100000001)"
python -c "100000000 in range(100000001)" 4.00s user 1.47s system 99% cpu 5.527 total
$ time python3 -c "100000000 in range(100000001)"
python3 -c "100000000 in range(100000001)" 0.04s user 0.01s system 86% cpu 0.055 total如果把量级增高， Py2会出现 MemoryError, Py3也会以非常快的速度执行。所以猜测Py3没有生成列表.
先看下两个方法的区别.
Python2
Python
>>> dir(range)
['__call__', '__class__', '__cmp__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__self__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']Python3
Python
>>> dir(range)
['__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'count', 'index', 'start', 'step', 'stop']可以看出有部分方法和属性的区别， 很明显Py3增强了 range 函数. 其实需要注意的是__contains__, 这个函数支持了in和not in运算符, 所以完全可以通过，判断100000000是否大于开始数字和结束数字即可完成in和not in运算.
如何用Py2实现Py3的range
注意代码中的__contains__方法.
Python
class my_range(object):
def __init__(self, start, stop=None, step=1):
if stop is None:
start, stop = 0, start
self.start, self.stop, self.step = start, stop, step
if step < 0:
lo, hi = stop, start
else:
lo, hi = start, stop
self.length = ((hi - lo - 1) // abs(step)) + 1
def __iter__(self):
current = self.start
if self.step < 0:
while current > self.stop:
yield current
current += self.step
else:
while current < self.stop:
yield current
current += self.step
def __len__(self):
return self.length
def __getitem__(self, i):
if i < 0:
i += self.length
if 0 <= i < self.length:
return self.start + i * self.step
raise IndexError('Index out of range: {}'.format(i))
def __contains__(self, num):
if self.step < 0:
if not (self.stop < num <= self.start):
return False
else:
if not (self.start <= num < self.stop):
return False
return (num - self.start) % self.step == 0整理翻译于StackoverFlow
本文参与 腾讯云自媒体同步曝光计划，分享自作者个人站点/博客。
如有侵权请联系 cloudcommunity@tencent.com 删除
评论
登录后参与评论
推荐阅读
目录
腾讯云开发者
