virtualenv简介和安装

virtual是Github上的一个项目，按照它的原话就是『Python虚拟环境的构建者』，这是它的项目地址：Virtual Python Environment builder

这里简单介绍下它的工作原理：virtualenv把运行Python程序必须的基本环境，包括二进制Python自身、Python标准库、pip安装器，以及至关重要的site-packages目录，全部拷贝一份到一个完全隔离的目录下，这个目录就是你的独立开环境

在项目首页最下面有安装教程的超链接：Installation，你可以简单敲pip命令进行安装，这是最简便的方法

pip install virtualenv

另外还用第二种方法：把项目整个当下来，然后手动安装

# Use virtualenv globally

$ curl -O https://pypi.python.org/packages/source/v/virtualenv/virtualenv-X.X.tar.gz

$ tar xvfz virtualenv-X.X.tar.gz

$ cd virtualenv-X.X

$ [sudo] python setup.py install

# Use virtualenv locally

$ curl -O https://pypi.python.org/packages/source/v/virtualenv/virtualenv-X.X.tar.gz

$ tar xvfz virtualenv-X.X.tar.gz

$ cd virtualenv-X.X

$ python virtualenv.py myVE

事实上你需要全局安装的Python套件只有两个，即pip和virtualenv，如果 把virtualenv包括的pip算进去，那其实只要安装一个virtualenv已足矣

使用virtualenv创建独立项目

在安装好virtualenv后，就可以创建隔离环境的Python项目了，下面以demo这个项目为例

1. 创建项目根目录，命名为demo并进入该目录

➜  ~ mkdir demo 

➜  ~ cd demo 

➜  demo

2. 使用virtualenv命令，建议加上–no-site-packages选项

➜  demo virtualenv --no-site-packages venv 

Using base prefix '/Library/Frameworks/Python.framework/Versions/3.6'

New python executable in /Users/macbookpro/demo/venv/bin/python3.6

Also creating executable in /Users/macbookpro/demo/venv/bin/python 

Installing setuptools, pip, wheel...done.

3. 如果想要手动指定Python版本，请使用–python=$PYTHON_VERSION选项

➜  demo virtualenv --python=python2.7 --no-site-packages venv1 

Running virtualenv with interpreter /usr/local/bin/python2.7

New python executable in /Users/macbookpro/demo/venv1/bin/python2.7

Also creating executable in /Users/macbookpro/demo/venv1/bin/python 

Installing setuptools, pip, wheel...done.

4. 你甚至可以指定系统没有安装的Python版本，比如我这里的Python3.7，但是绝对不要想当然的填写Pyhton版本号否则会报错“doesn’t exist”

➜  demo virtualenv --python=python3.7 --no-site-packages venv2 

Running virtualenv with interpreter /usr/local/bin/python3.7

Using base prefix '/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7'

/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/virtualenv.py:1041: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses  

import imp

New python executable in /Users/macbookpro/demo/venv2/bin/python3.7

Also creating executable in /Users/macbookpro/demo/venv2/bin/python 

Installing setuptools, pip, wheel...done. 

➜  demo virtualenv --python=python4.0 --no-site-packages venv3 

The path python4.0 (from --python=python4.0) does not exist

5. 在新建的venv目录下，重点关注bin目录，它包括了pip管理器和python对应版本的解释器Pythonx.x.

➜  venv ls 

bin                include            lib                pip-selfcheck.json

➜  venv cd bin 

➜  bin ls 

activate               easy_install          pip3.6           python3.6

activate.csh         easy_install-3.6   python           wheel 

activate.fish         pip                       python-config 

activate_this.py    pip3                    python3

➜  demo venv/bin/pip install requests 

Collecting requests

  Downloading https://files.pythonhosted.org/packages/65/47/7e02164a2a3db50ed6d8a6ab1d6d60b69c4c3fdf57a284257925dfc12bda/requests-2.19.1-py2.py3-none-any.whl (91kB)

    100% |████████████████████████████████| 92kB 138kB/s

Collecting idna<2.8,>=2.5 (from requests)

  Downloading https://files.pythonhosted.org/packages/4b/2a/0276479a4b3caeb8a8c1af2f8e4355746a97fab05a372e4a2c6a6b876165/idna-2.7-py2.py3-none-any.whl (58kB)

    100% |████████████████████████████████| 61kB 52kB/s

Collecting urllib3<1.24,>=1.21.1 (from requests)

  Downloading https://files.pythonhosted.org/packages/bd/c9/6fdd990019071a4a32a5e7cb78a1d92c53851ef4f56f62a3486e6a7d8ffb/urllib3-1.23-py2.py3-none-any.whl (133kB)

    100% |████████████████████████████████| 143kB 29kB/s 

Collecting chardet<3.1.0,>=3.0.2 (from requests)

  Downloading https://files.pythonhosted.org/packages/bc/a9/01ffebfb562e4274b6487b4bb1ddec7ca55ec7510b22e4c51f14098443b8/chardet-3.0.4-py2.py3-none-any.whl (133kB)

    100% |████████████████████████████████| 143kB 53kB/s 

Collecting certifi>=2017.4.17 (from requests)

  Downloading https://files.pythonhosted.org/packages/7c/e6/92ad559b7192d846975fc916b65f667c7b8c3a32bea7372340bfe9a15fa5/certifi-2018.4.16-py2.py3-none-any.whl (150kB)

    100% |████████████████████████████████| 153kB 41kB/s 

Installing collected packages: idna, urllib3, chardet, certifi, requests 

Successfully installed certifi-2018.4.16 chardet-3.0.4 idna-2.7 requests-2.19.1 urllib3-1.23

6. 用virtual内置pip安装的包被放在lib目录下

➜  demo venv/bin/pip show requests

Name: requests

Version: 2.19.1

Summary: Python HTTP for Humans. 

Home-page: http://python-requests.org

Author: Kenneth Reitz 

Author-email: me@kennethreitz.org

License: Apache 2.0

Location: /Users/macbookpro/demo/venv/lib/python3.6/site-packages

Requires: idna, certifi, chardet, urllib3 

Required-by:

7. 为了减少打字，可激活activate文件，这样原来的venv/bin/pip就要写pip，代替了系统原来的pip命令，不用时激活deactivate命令即可

➜  demo source venv/bin/activate

(venv) ➜  demo pip list

Package    Version   

---------- ---------

certifi    2018.4.16

chardet    3.0.4    

idna       2.7      

pip        10.0.1   

requests   2.19.1   

setuptools 40.0.0   

urllib3    1.23    

wheel      0.31.1  

 (venv) ➜  demo pip uninstall requests 

Uninstalling requests-2.19.1:

   Would remove:

    /Users/macbookpro/demo/venv/lib/python3.6/site-packages/requests-2.19.1.dist-info/*

    /Users/macbookpro/demo/venv/lib/python3.6/site-packages/requests/* 

Proceed (y/n)? y  

Successfully uninstalled requests-2.19.1

(venv) ➜  demo pip list

Package    Version   

---------- ---------

certifi    2018.4.16

chardet    3.0.4    

idna       2.7      

pip        10.0.1   

setuptools 40.0.0   

urllib3    1.23     

wheel      0.31.1   

(venv) ➜  demo 

 (venv) ➜  demo deactivate 

 ➜  demo

8. pip和virtualenv合作使用起来很爽，pip使用-r参数指定requirement文件

pip install -r requirements.txt

ok，这样基本的隔离Python开发环境就被创建出来啦～关于virtualenv暂就讲到这里，还有些比较方便的功能有待大家共同探索^ ^