Python-Virtualenv

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Before using virtualenv, the default interpreter of ubuntu is python2.7, and it is already installed in /usr/lib/python3ipython3 and 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]:

use

Due to some compatibility issues, the default python version on the computer can only use python2.7, so create The command must be additionally used -pSpecify the interpreter

$ 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.

Activate the virtual environment

$ source venv/bin/activate

Now you can see an extra ## in front of the prompt #venv, represents the successful creation of the virtual environment

(venv) ~/my_project_folder $ ipython3

Practice it, the virtual environment is isolated from the actual environment

# 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'

Note that there is no need to use 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

Request now It has been used correctly

(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

Now ipython can also be used correctly

(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]:

Exit

(venv) ~/my_project_folder $ deactivate

The principle is very simple, that is, copy the system Python to the virtualenv environment , when using the command

source venv/bin/activate to enter a virtualenv environment, virtualenv will modify the relevant environment variables so that the commands python and pip point to the current virtualenv environment.

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