注释

在使用virtualenv前ubuntu默认的解释器是python2.7，而且/usr/lib/python3里面已经安装好了ipython3和requests

$ python
Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
[GCC 5.4.0 20160609] on linux2
TyPE "help", "copyright", "credits" or "license" for more information.
>>>

$ ipython3    
Python 3.5.2 (default, Nov 17 2016, 17:05:23) 
Type "copyright", "credits" or "license" for more information.

IPython 5.1.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: import requests

In [2]:

使用

由于一些兼容性问题，电脑上默认的python版本只能只能使用python2.7，所以创建命令要另外使用-p指定解释器

$ mkdir my_PRoject_folder; cd my_project_folder

# 创建虚拟环境
$ virtualenv -p /usr/bin/python3 venv
Running virtualenv with interpreter /usr/bin/python3
Using base prefix '/usr'
New python executable in /home/ormsf/my_project_folder/venv/bin/python3
Also creating executable in /home/ormsf/my_project_folder/venv/bin/python
Installing SETUPtools, pkg_resources, pip, wheel...done.

激活虚拟环境

$ source venv/bin/activate

现在可以看到提示符前面多了一个venv，代表虚拟环境创建成功

(venv) ~/my_project_folder $ ipython3

实践一下，虚拟环境和实际的环境隔离的

# 无法使用ipython3
(venv) ~/my_project_folder $ ipython3  
Traceback (most recent call last):
  File "/usr/bin/ipython3", line 4, in <module>
    from IPython import start_ipython
ImportError: No module named 'IPython'

# 默认的解释器已经变成了python3
(venv) ~/my_project_folder $ python
Python 3.5.2 (default, Nov 17 2016, 17:05:23) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.

# 无法使用requests
>>> import requests
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named 'requests'

注意不需要使用piP3

(venv) ~/my_project_folder $ pip install requests
Collecting requests
  Downloading requests-2.13.0-py2.py3-none-any.whl (584kB)
    100% |████████████████████████████████| 593kB 1.3MB/s 
Installing collected packages: requests
Successfully installed requests-2.13.0

现在request已经能够正确使用了

(venv) ~/my_project_folder $ python
Python 3.5.2 (default, Nov 17 2016, 17:05:23) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import requests
>>> 

(venv) ~/my_project_folder $ pip install ipython

现在ipython也已经能够正确使用了

(venv) ~/my_project_folder $ ipython
Python 3.5.2 (default, Nov 17 2016, 17:05:23) 
Type "copyright", "credits" or "license" for more information.

IPython 5.1.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: 

退出

(venv) ~/my_project_folder $ deactivate

原理很简单，就是把系统Python复制一份到virtualenv的环境，用命令source venv/bin/activate进入一个virtualenv环境时，virtualenv会修改相关环境变量，让命令python和pip均指向当前的virtualenv环境。