How to install virtual environment virualenv in python

virtualenv is a tool for creating isolated Python environments. virtualenv creates a folder containing all the necessary executable files to use the packages required for Python projects.

After installing python, pip, setuptools and other tools, you can create a virualenv virtual environment. This tool, similar to a virtual machine, can run multiple different versions of python programs on the same computer and interact with each other. It does not affect it. You can exit or delete it when not in use. It is a very good development tool.

1. Install virtualenv

#安装python
brew install python
curl https://bootstrap.pypa.io/ez_setup.py -o - | sudo python
sudo easy_install pip
# 使用pip安装virtualenv
pip install virtualenv

2. Use of virtualenv

#创建一个叫做pythonEnv的新环境
virtualenv pythonEnv
#激活再使用
cd pythonEnv
source bin/activate
#退出环境
deactivate

3. Use virtualenvwrapper to manage the virtual environment

Install virtualenvwrapper

pip install virtualenvwrapper

Configure environment variables:

vim ~/.bash_profile

# Virtualenv/VirtualenvWrapper
source /usr/local/bin/virtualenvwrapper.sh

Save and exit

Then execute the following command to let the system reload the configuration

source ~/.bash_profile

Create environment

mkvirtualenv pythonEnv #在 ~/Envs 中创建 pythonEnv文件夹
mkvirtualenv python3Env -p python3.5 #创建python3.5的环境

Switch environment:

workon pythonEnv

Exit the environment:

deactivate

Delete the environment:

rmvirtualenv pythonEnv

Others

1. Other commands

lsvirtualenv #List all environments.

cdvirtualenv # Navigate to the directory of the currently active virtual environment, e.g. so you can browse its site-packages.

cdsitepackages #Similar to the above, but directly enters the site-packages directory.

lssitepackages #Display the contents of the site-packages directory.

2. When using the easy_install command to install pip, an ImportError: No module named extern error occurs

Cause: The extern module of python2.7.12 that comes with mac is not installed

Solution:

#Download extern from https://pypi.python.org/pypi/extern/0.1.0, then unzip and install

tar zxf extern-0.1.0.tar .gz && python setup.py install

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