Linux command--virtualenv

Virtualenv can build a virtual and stand-alone Python environment, allowing each project environment to be isolated from other projects, keeping the environment clean, and resolving package conflict issues.

First, install the virtualenv

Virtualenv is actually a python package, so we can install it with Easy_install or PIP. The installation methods on the CentOS system are described below.

using the Easy_install installation method :

[[email protected] ~]# Yum install python-setuptools python-devel[[email protected] ~]# easy_install virtualenv

Use the PIP installation method:

[[email protected] ~]# easy_install pip[[email protected] ~]# pip install virtualenv

Use the Yum installation method:

[email protected] ~]# Yum install python-virtualenv

Ii. Creating a Python virtual environment

To create a Python virtual environment using the virtualenv command:virtualenv [Virtual environment name]

[Email protected] ~]# virtualenv env1new python executable in env1/bin/pythoninstalling setuptools, Pip...done.

Once executed, a folder with the same name as the virtual environment is generated locally.
If you have different versions of Python installed in your system, you can use the --python parameter to specify the Python version of the virtual environment:

[Email protected] ~]# virtualenv--python=/usr/local/python-2.7.8/bin/python2.7 env1running virtualenv with Interpreter/usr/local/python-2.7.8/bin/python2.7new python executable in env1/bin/python2.7also creating executable In Env1/bin/pythoninstalling Setuptools, Pip...done.

Measured by default, the virtual environment does not rely on the global site-packages of the system environment. For example, the system environment installed MYSQLDB module, in the virtual environment import MySQLdb will prompt importerror. If you want to rely on a third-party package for your system environment, you can use parameter--system-site-packages. Alternatively, you can use the Virtualenvwrapper toggleglobalsitepackages command to control whether the current environment uses global site-packages.

[Email protected] ~]# virtualenv--system-site-packages env1new python executable in env1/bin/pythoninstalling Setuptools, Pip...done.

Third, start the virtual environment

Enter the virtual environment directory and start the virtual environment as follows:

[Email protected] ~]# CD Env1/[[email protected] env1]# source Bin/activate (ENV1) [[email protected] env1]# Python-vpytho N 2.7.8

At this point the command line will be preceded by a parenthesis with the name of the virtual environment in parentheses. All modules installed later Easy_install or PIP will be installed in the virtual environment directory.

Iv. exiting the virtual environment

Exiting the virtual environment: deactivate

(ENV1) [Email protected] env1]# Deactivate[[email protected] env1]#

V. Use of Virtualenvwrapper

Virtualenvwrapper is a virtualenv extension tool that makes it easy to create, delete, copy, and switch between different virtual environments.

1. Installing Virtualenvwrapper

[Email protected] ~]# Easy_install virtualenvwrapper or: [[email protected] ~]# pip install Virtualenvwrapper

Note: This is not an operation in a virtual environment.

Create a folder to hold all the virtual environments:

[Email protected] ~]# mkdir ~/workspaces

Set the environment variable and add the following two lines to the ~/.BASHRC.

[Email protected] ~]# export Workon_home=~/workspaces[[email protected] ~]# source/usr/local/bin/ virtualenvwrapper.sh

Then you can use the Virtualenvwrapper. 2. Create a virtual Environment: mkvirtualenv [Virtual Environment name]

[Email protected] ~]# mkvirtualenv env1new python executable in env1/bin/pythoninstalling setuptools, Pip...done. (ENV1) [Email protected] ~]# mkvirtualenv env2new python executable in env2/bin/pythoninstalling setuptools, Pip...done. (ENV2) [Email protected] ~]#

Note: mkvirtualenv can use virtualenv parameters, such as--python, to specify the Python version. Once the virtual environment is created, it is automatically switched to this virtual environment. The virtual Environment directory is in Workon_home.

3. List Virtual environments: Lsvirtualenv-b

(ENV2) [Email protected] ~]# Lsvirtualenv-benv1env2

4. Start or switch Virtual environments: Workon [virtual Environment name]

(ENV2) [Email protected] ~]# Workon env1 (ENV1) [[email protected] ~]# echo $VIRTUAL _env/root/workspaces/env1

5. Check which packages are installed in the environment: lssitepackages

(ENV2) [Email protected] ~]# lssitepackageseasy_install.py  pip                  pkg_resources.py  setuptools_markerlib       Pip-1.5.4.dist-info  __pycache__       setuptools-2.2.dist-info

6. Enter the current environment directory: cdvirtualenv [subdirectory name]

(ENV1) [Email protected] ~]# cdvirtualenv (ENV1) [[email protected] env1]# pwd/root/workspaces/env1 (ENV1) [[email protected] env1]# Cdvirtualenv Bin (env1) [[email protected] bin]# Pwd/root/workspaces/env1/bin

Enter the Site-packages directory for the current environment: cdsitepackages [subdirectory name]

(ENV1) [Email protected] env1]# cdsitepackages (ENV1) [[email protected] site-packages]# pwd/root/workspaces/env1/lib/ Python2.6/site-packages (ENV1) [[email protected] site-packages]# cdsitepackages pip (env1) [[email protected] pip]# pwd/ Root/workspaces/env1/lib/python2.6/site-packages/pip

7. Control whether the environment uses global SITE-PACKAGES:TOGGLEGLOBALSITEPACKAGES8. Replicating a virtual Environment: cpvirtualenv [Source] [dest]

[Email protected] ~]# cpvirtualenv env1 env3copying env1 as Env3 ... (ENV3) [Email protected] ~]#

9. Exit the virtual environment: DEACTIVATE10. Delete Virtual Environment: rmvirtualenv [Virtual Environment name]

[Email protected] ~]# rmvirtualenv env2removing env2 ...

Vi. relevant points of knowledge

As you can see from this diagram, Windows-like EXE programs, in fact, python2.7, python3.4, and python3.4m are executable files. So as long as the/usr/bin is added to the environment variable path, in any directory can execute the three executable program, run a different version of Python.

For simplicity, a soft link is generated for each of the three executables. If you delete the current Python soft link and re-establish a soft link and point it to python3.4, running the python command at the terminal launches the python3.4 executable program.

Here's a question:

At the time of establishing the virtualenv, the Python version of the virtual environment is executed through--python, which can be seen in the directory of the virtual environment, but Python is found in the/usr/bin directory of the real system through the which Python command.

Linux command--virtualenv