小编Zwe*_*end的帖子

我尝试使用virtualenvwrapper创建一个兼具python2和python3的virtualenv

每个virtualenv与python2和python3通过Homebrew我希望这将工作:

(virtualenv的名字是'double')

mkvirtualenv double -p `which python`
mkvirtualenv double -p `which python3`

它提到了这一点

Not overwriting existing python script both/bin/python (you must use both/bin/python3.4)

但这似乎并非如此.打字python python2.7 python3并python3.4全部启动python3.4翻译.

我写了自己的矢量类:

#! /usr/bin/env python3

class V:
    """Defines a 2D vector"""
    def __init__(self,x,y):
        self.x = x
        self.y = y
    def __add__(self,other):
        newx = self.x + other.x
        newy = self.y + other.y
        return V(newx,newy)
    def __sub__(self,other):
        newx = self.x - other.x
        newy = self.y - other.y
        return V(newx,newy)
    def __str__(self):
        return "V({x},{y})".format(x=self.x,y=self.y)

我想定义V(0,0)是一个空向量,这样就可以了:(第一种情况应该返回"Vector为空")

v = V(0,0)
u = V(1,2)

if u:
    print (u)
else:
    print("Vector is empty")

if v:
    print(v)
else:
    print("Vector is empty")