1. virtualenv

Python2 and Python3 are supportive manner

1.1 Installation

pip install virtualenv

1.2 Creating project

cd my_project_folder
virtualenv my_project

Specifies the python version 1.3

virtualenv -p /usr/bin/python2.7 my_project

Or adding an environment variable configuration

export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python2.7

1.4 activate the virtual environment

(Linux) source my_project/bin/activate

(Windows) my_project\Scripts\activate

1.5 Exit environment

(Linux) my_project/bin/deactivate

(Windows) my_project\Scripts\deactivate.bat

1.6 virtualenv Common command options

virtualenv [the OPTIONS] dest_dir 

Options: 
-version Display version information. 
- H, -help display help information.
- v, -verbose increase output of background information.
- Q, -quiet control information output from the background.
PYTHON_EXE -p, -python = PYTHON_EXE　　
　　　　　　　　　specify the Python interpreter 
- the Clear 　　　　　　Clear virtual environment dependencies, initialize the environment. 
-System -site- Packages Standard Package 
　　　　　　　　　using the current library on the main Python installed. 
-Always - Copy not and will not use a symbolic link, copy the file directly. 
The -no -setuptools the Do not install setuptools in at The new new 
virtualenv. The -no -pip the Do not install PIP in the new virtualenv.
–no-wheel　　　　Do not install wheel in the new virtualenv.

1.7 virtualenv Related Extensions

virtualenvwrapper

virtualenv expansion pack, can easily manage virtualenv

1.7.1 Installation

WORKON_HOME environment variable to specify the position of the virtual environment

(Linux)
pip install virtualenvwrapper
export WORKON_HOME=~/Envs
source /usr/local/bin/virtualenvwrapper.sh

(Windows) 
PIP install virtualenvwrapper- win 
WORKON_HOME default is % USERPROFILE% Envs

1.7.2 Basic Usage

Create a virtual environment

mkvirtualenv myenv

Switch to the virtual environment

workon myenv

Virtual environment and project separately

mkproject my_project 
virtual environment WORKON_HOME, the items in the PROJECT_HOME

Exit Virtual Environment

deactivate

Delete the virtual environment

rmvirtualenv myenv

Other uses

lsvirtualenv enumerate all environments. 
cdvirtualenv [subdir] to navigate to the current directory active virtual environment 
cdsitepackages [subdir] and similar to the above, but is direct access to the Site - packages directory 
lssitepackages display Site - Content packages directory 
showvirtualenv [ env ] displays the specified environment details 
cpvirtualenv [source] [dest] a copy of the virtual environment 
allvirtualenv implementation of a unified command for the current virtual environment 
add2virtualenv [ dir ] [ dir ] is added to the directory specified by the environment currently used path, which is often used 
for multiple project which use a large library of case 
toggleglobalsitepackages -q controls the current environment is to use global directory of sitepackages

virtualenv-burrito
equivalent virtualenv + virtualenvwrapper, but only supports python 2

autoenv
When .env into a directory containing, autoenv automatically activates the environment
pip install autoenv

2. venv

Python3 supportive manner, and formerly known as pyvenv, python 3.6 deprecated

2.1 to create a virtual environment

python3 -m venv /path/to/new/virtual/environment

2.2 Command Help

-m Venv python3 - H 

Usage: Venv [ -h] [--system-Site-Packages Standard Package] [--symlinks | --copies] [- the Clear ] 
            [ --upgrade] [--without-PIP] [- - prompt pROMPT] 
            ENV_DIR [ENV_DIR ...] 
Creates Virtual Environments Python in One or More target Directories. 
Positional arguments The: 
  ENV_DIR to the Create A Directory at The Environment in . 
optional arguments The:
   -h, - help help
   --system-site -packages access to the virtual environment system site- rights packages directory
   - when symlinks when the system is not a symbolic link to the default way, try to use symbolic links instead of copying.
  - copies try to use symbolic links instead of copying, even if symbolic link is the platform's default mode.
  - the Clear                  before the virtual environment to create, delete virtual environment directory that already exists.
  - upgrade the current python, upgrade the virtual environment directory.
  --without- pip pip skipped upgrades or installations
   - prompt PROMPT prefix for the environment to provide a prompt 

Once AN Environment has been the Created, you May of an activate td width = wish to IT, by EG 
Sourcing AN of an activate Script in the ITS bin Directory.

2.3 virtual environments on different platforms activation method

Activation Method
Platform	Shell	Command activates the virtual environment
Posix	bash/zsh	$ source /bin/activate
	fish	$ . /bin/activate.fish
	csh/tcsh	$ source /bin/activate.csh
Windows	cmd.exe	C:> \Scripts\activate.bat
Windows	PowerShell	C:> \Scripts\Activate.ps1

Transfer: https://blog.csdn.net/yezhenquan123/article/details/79313110

python-virtualenv and venv