conda能够实现多个环境共存原因的感悟

conda能够实现多个环境共存原因：


首先查看我目前有多少个环境：
conda info —envs
结果如下：
# conda environments:
#
python27                 /Users/zj_macbook/anaconda/envs/python27
python3               *  /Users/zj_macbook/anaconda/envs/python3
root                     /Users/zj_macbook/anaconda



用 source activate <environment name>激活不同的python环境
三个环境下的PATH的值分别为：
root:
~/anaconda/bin:
/opt/local/bin:
/opt/local/sbin:
/usr/local/bin:
/usr/bin:
/bin:
/usr/sbin:
/sbin:
/Library/TeX/texbin


python27：
/Users/zj_macbook/anaconda/envs/python27/bin:
~/anaconda/bin:
/opt/local/bin:
/opt/local/sbin:
/usr/local/bin:
/usr/bin:
/bin:
/usr/sbin:
/sbin:
/Library/TeX/texbin


python3：
/Users/zj_macbook/anaconda/envs/python3/bin:
~/anaconda/bin:
/opt/local/bin:
/opt/local/sbin:
/usr/local/bin:
/usr/bin:
/bin:
/usr/sbin:
/sbin:
/Library/TeX/texbin

从这里可以看出conda把自己当前的环境写入PATH，这样在终端调用的部分工具都是当前环境目录下的工具。

比如，在每一个不同的python环境下都有一个对应版本的pip，当使用该pip时，pip会把库文件安装在当前环境的python目录下。

而brew则不同，brew安装在/usr/local/bin中，调用brew安装库文件时brew会把它们安装在/usr/local/lib/python2.7/site-packages中，这时conda中的python是引用不了brew安装的库文件的

三个环境下的python的sys.path的值分别为：


root:
['', 
'/Users/zj_macbook/anaconda/lib/python27.zip',
'/Users/zj_macbook/anaconda/lib/python2.7', 
'/Users/zj_macbook/anaconda/lib/python2.7/plat-darwin', 
'/Users/zj_macbook/anaconda/lib/python2.7/plat-mac', 
'/Users/zj_macbook/anaconda/lib/python2.7/plat-mac/lib-scriptpackages', 
'/Users/zj_macbook/anaconda/lib/python2.7/lib-tk', 
'/Users/zj_macbook/anaconda/lib/python2.7/lib-old', 
'/Users/zj_macbook/anaconda/lib/python2.7/lib-dynload', 
'/Users/zj_macbook/anaconda/lib/python2.7/site-packages', 
'/Users/zj_macbook/anaconda/lib/python2.7/site-packages/Sphinx-1.4.6-py2.7.egg', 
'/Users/zj_macbook/anaconda/lib/python2.7/site-packages/aeosa', 
'/Users/zj_macbook/anaconda/lib/python2.7/site-packages/setuptools-27.2.0-py2.7.egg']


python27:
['', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python27.zip', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/plat-darwin', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/plat-mac', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/plat-mac/lib-scriptpackages', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/lib-tk', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/lib-old', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/lib-dynload', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/site-packages', 
'/Users/zj_macbook/anaconda/envs/python27/lib/python2.7/site-packages/setuptools-27.2.0-py2.7.egg']


python3:
['', 
'/Users/zj_macbook/anaconda/envs/python3/lib/python36.zip', 
'/Users/zj_macbook/anaconda/envs/python3/lib/python3.6', 
'/Users/zj_macbook/anaconda/envs/python3/lib/python3.6/lib-dynload', 
'/Users/zj_macbook/anaconda/envs/python3/lib/python3.6/site-packages', 
'/Users/zj_macbook/anaconda/envs/python3/lib/python3.6/site-packages/setuptools-27.2.0-py3.6.egg']


这里可以看出不同环境下的python的sys.path中的路径的是当前环境下的路径，保证了导入的python包只能是当前环境下的。