Python-Virtualenv

註釋

在使用virtualenv前ubuntu默認的解釋器是python2.7，並且/usr/lib/python3裏面已經安裝好了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

因爲一些兼容性問題，電腦上默認的python版本只能只能使用python2.7，因此建立命令要另外使用-p指定解釋器

$ mkdir my_project_folder; cd my_project_folder

# 建立虛擬環境
$ 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.

激活虛擬環境

$ source venv/bin/activate

如今能夠看到提示符前面多了一個venv，表明虛擬環境建立成功

(venv) ~/my_project_folder $ ipython3

實踐一下，虛擬環境和實際的環境隔離的

# 沒法使用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'

# 默認的解釋器已經變成了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.

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

注意不須要使用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

如今request已經可以正確使用了

(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

如今ipython也已經可以正確使用了

(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

原理很簡單，就是把系統Python複製一份到virtualenv的環境，用命令source venv/bin/activate進入一個virtualenv環境時，virtualenv會修改相關環境變量，讓命令python和pip均指向當前的virtualenv環境。