Detailed graphic and text explanation on how to achieve the coexistence of multiple versions of Python in virtualenv

Virtualenv is used to create an independent Python environment. Multiple Pythons are independent of each other and do not affect each other. It can: 1. Install new packages without permissions 2. Different applications can use different package versions 3. Package upgrades Does not affect other applications

virtualenv creates an environment with its own installation directory. This environment does not share libraries with other virtual environments, and can easily manage python versions and manage python libraries. Mainly solve the problem of environmental conflicts between different projects.

Tips

Some development packages may be downloaded incorrectly when downloading. If domestic mirror downloads are configured, the chance of errors will be greatly reduced. . Using the mirror source is very simple, just specify it with -i: <br>

sudo pip install -i https://pypi.douban.com/simple/ saltTesting

For example, now you need to install the django environment<br>

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Virtualenv use

If you need to uninstall django, you can use pip uninstall django

##virtualenvAfter basic use and installation, you need to create a new virtualenv Independent environment, you can check its help command for details:

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Basic command

Commonly used parameters are:

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-p: Specify a version of the python environment; usually used when multiple python versions are installed in your system; by default virtualenv will give priority to its host python environment, that is, where it is installed Under the python version, which version will be selected by default as the default python isolation environment.

--no-site-packages: Do not use the python installation package of the system environment, that is, the installation package of the real python environment cannot be used in the isolation package; this option is the default in the current version. <br>--system-site-packages: Contrary to the above, it enables the isolated environment to access the python installation package of the system environment <br>--distribute: Copy a branch of the python environment. By default, setup, pip, wheel and other basics will be installed. Module <br>

virtualenv test, use this command to create a Python environment under the specified path, which is consistent with the system environment by default. If you want to enter the virtual environment, you need to enter the test/Scripts/ folder and run activate.bat. Under Linux, in the bin directory, the running command is source xx/xx/activate and the exit command is deactivate.bat

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Specify other Python environments

virtualenv -p C:\Python27\python2.exe py2

Quick configuration

Virtual environment management tool based on virtualenv

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pip install virtualenvwrapper-win<br>

After the installation is complete, configure the environment variables, such as As shown in the figure.

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WORKONHOME<br>

After that, you can use workon to display the virtual environment, mkvirtualenv xx creates the virtual environment, and workon xxx enters the virtual environment

Others

1. When using pip to install, you may be prompted that some files cannot be found. You can go here to find the whl file, mainly for Windows user files. After downloading, enter the virtual environment and use pip to install You can use

2. mkvirtualenv to create other versions of virtual environments,

   mkvirtualenv --python=C:\Python27\python2.exe py2scrapy

3. After installing virtualenvwrapper under Linux, you need to configure it. First find virtualenvwrapper.sh

##Modify the configuration file<br>

Modify content<br>

Reload configuration

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