How the Python virtual environment virtualenv is used

Time:2022-9-20

Learn about virtual environments

If you want to develop multiple different projects on one machine, you need to use different versions of the same package. If you also use the above command to install or update in the same directory, other projects must not be able to run. How to do it?

Solution: Virtual Environment

So what is a virtual environment?

The virtual environment is actually a copy of the real python environment, so that we install packages in the copied python environment without affecting the real python environment. By establishing multiple virtual environments, developing projects in different virtual environments achieves isolation between projects.

Installation of virtual environment library

We use virtualenv here to create a virtual environment.
pip's default source installation of the third library will be a bit slow, you can configure other mirror sources.

Install on Windows

existcmdwindow to see if the system is installedvirtualenv


virtualenv --version

pip install virtualenv


pip3 install virtualenv
pip3 install virtualenvwrapper-win

virtualenvwrapper-winVirtual environment extension package (convenient instruction)

virtual environment creation

existcmdCreate a python3 virtual environment under the windowpy_django


mkvirtualenv -p python3 py_django

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Notice:
The virtual environment created by Windows defaults toC:\Users\Administrator\Envs, Administrator represents the user my current computer is using, yours may be under other users, if you need to specify the storage path of the created virtual environment, you can add it in the system environment variable of the computerWORKON_HOMEsystem variable

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Install on Linux

Install a virtual environment


sudo pip3 install virtualenv
sudo pip3 install virtualenvwrapper

GuaranteedLinuxTherePython3environment of.
After installing the virtual environment, enter the following command to test


mkvirtualenv test

If the prompt cannot be foundmkvirtualenvcommand, environment variables must be configured

# 1. Create a directory to store the virtual environment
mkdir $HOME/.virtualenvs

# 2. Open ~/.bashrc file
vim ~/.bashrc

# 2.1 Add the following two lines
export WORKON_HOME=$HOME/.virtualenvs
source /usr/local/bin/virtualenvwrapper.sh

# 3. Run
source ~/.bashrc

WORKON_HOMEThe location where the virtual environment directory is stored can be set independently.

Create a virtual environment


mkvirtualenv py_flask

Enter the virtual environment


workon py_flask

Exit the virtual environment

If the environment is a real environment, it will promptdeactivate: command not found


deactivate py_flask

virtual environment directives

The instructions are the same on both Windows and Linux platforms.

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Notice:

Exit first: deactivate
Then delete: rmvirtualenv virtual environment name

Virtual Environment Summary

1. Using a virtual environment will not mess up many libraries of the main interpreter

2. For example, if you install Flask in a separate virtual environment, you will know all the libraries used in subsequent development. Usepip freezeThe command knows what environment your project needs, and there are many libraries that are not used by the project in the main interpreter. Using a virtual environment to deploy to the server is convenient for environment configuration, and there is no need to filter the required libraries one by one.

Use in a virtual environment

  • pip freezeCheck the library environment required by the project.
  • pip freeze > requirements.txtLibrary information required for exporting the project.
  • pip install -r requirements.txBulk install libraries required by the project.

3. Develop multiple projects on the same machine, but encounter inconsistent versions of the same library required by the project. Therefore, the virtual environment is used to isolate each project independently, and different version libraries can be used separately.

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