Python Learning Note 02:python virtual environment

Information reference: Liaoche's official website https://www.liaoxuefeng.com/wiki/0014316089557264a6b348958f449949df42a6d3a2e542c000/ 001432712108300322c61f256c74803b43bfd65c6f8d0d0000

I. BACKGROUND

If the system has only one version of Python3 installed--3.4, if we want to develop multiple applications at the same time, then these applications will share a python, is installed in the system of Python 3, all third-party packages will be pip installed into the Python3 site-packages Directory. What if application a requires Jinja 2.7 and application B needs Jinja 2.6?

In this case, each app may need to have a "standalone" Python runtime environment. Virtualenv is a python run environment that is used to create a "quarantine" for an application.

Second, virtualenv installation

$ PIP3 Install virtualenv

　　

Iii. What should I do when I need a separate running Python environment?

1. Create a Directory

mac:~ michael$ mkdir myprojectmac:~ michael$ cd myproject/mac:myproject michael$

2. Create a stand-alone python environment namedvenv

Mac:myproject michael$ virtualenv--no-site-packages venvusing base prefix '/usr/local/.../python.framework/versions/ 3.4 ' New python executable in venv/bin/python3.4also creating executable in Venv/bin/pythoninstalling Setuptools, Pip, whe El ... Done.

Command virtualenv to create a standalone Python runtime environment, we have added parameters --no-site-packages so that all third-party packages that have been installed into the system Python environment will not replicate, so that we get a "clean" without any third-party packages Python runtime environment.

The new Python environment is placed in the directory under the current directory venv . With venv This Python environment, you can source enter the environment:

Mac:myproject michael$ Source Venv/bin/activate (venv) Mac:myproject michael$

Notice that the command prompt is changed and has a (venv) prefix that indicates that the current environment is a venv python environment named.

The following normal installation of various third-party packages, and run the python command:

Install jinja2 ... Successfully installed JINJA2-2.7. 3 markupsafe-0.23(venv) mac:myproject michael$ python myapp.py ...

Under the environment, the system Python environment is not affected by the installation of the packages installed in venv pip venv this environment. In other words, the venv environment is created specifically for myproject this application.

3. Exit the current VENV environment

(venv) Mac:myproject michael$ Deactivate Mac:myproject michael$

At this point, we are back to normal environment, now pip or python all in the system Python environment.

Iv. Summary

It is entirely possible to create a separate Python runtime environment for each app, so that each app's Python environment can be isolated.

Virtualenv is the principle of creating a "stand-alone" Python environment: Copy the System python to a virtualenv environment, and source venv/bin/activate when you enter a virtualenv environment with a command, virtualenv modifies the relevant environment variables, allowing the command pythonand pip both point to the current virtualenv environment.

VIRTUALENV provides an isolated Python runtime environment for applications that resolves multiple versions of conflicts across different applications.

Python Learning Note 02:python virtual environment