130 lines
4.0 KiB
Markdown
130 lines
4.0 KiB
Markdown
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# 如何在 Python 中使用 Virtualenv
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> 原文：<https://www.pythonforbeginners.com/basics/python-virtualenv-usage>
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这篇文章将描述什么是 Virtualenv，以及你如何使用它。
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### 什么是 Virtualenv？
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```py
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Virtualenv is a tool to create isolated Python environments, it's perhaps the
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easiest way to configure a custom Python environment.
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Virtualenv allows you to add and modify Python modules without access to the
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global installation.
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```
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### 它是做什么的？
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```py
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The basic problem being addressed is one of dependencies and versions, and
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indirectly permissions.
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Imagine you have an application that needs version 1 of LibFoo, but another
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application requires version 2\.
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How can you use both these applications?
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If you install everything into /usr/lib/python2.7/site-packages (or whatever your
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platform’s standard location is), it’s easy to end up in a situation where you
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unintentionally upgrade an application that shouldn’t be upgraded.
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Or more generally, what if you want to install an application and leave it be?
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If an application works, any change in its libraries or the versions of those
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libraries can break the application.
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Also, what if you can’t install packages into the global site-packages directory?
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For instance, on a shared host.
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In all these cases, virtualenv can help you.
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It creates an environment that has its own installation directories, that doesn’t
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share libraries with other virtualenv environments
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```
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### 如何安装 Virtualenv？
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```py
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There are a few ways to install virtualenv on your machine.
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You can use either the source tarball, pip or by using easy_install.
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```
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##### 简单安装
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```py
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$ sudo easy_install virtualenv
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Searching for virtualenv
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Reading http://pypi.python.org/simple/virtualenv/
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Reading http://www.virtualenv.org
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Reading http://virtualenv.openplans.org
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Best match: virtualenv 1.8.2
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Downloading http://pypi.python.org/packages/source/v/virtualenv/virtualenv-1.8.2.tar.gz...
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processing virtualenv-1.8.2.tar.gz
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.....
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....
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Processing dependencies for virtualenv
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Finished processing dependencies for virtualenv
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```
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##### 源球安装
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```py
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Get the latest version from here: http://pypi.python.org/packages/source/v/virtualenv/
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wget http://pypi.python.org/packages/source/v/virtualenv/virtualenv-1.8.tar.gz
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tar xzvf virtualenv-1.8.tar.gz
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python virtualenv-1.8/virtualenv.py $HOME/env
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```
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##### Pip 安装
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```py
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pip install virtualenv
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```
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### 使用
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```py
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To create virtual environments, you can use the virtualenv command.
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Create an environment called "foobar":
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virtualenv foobar
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Activate the environment by sourcing its activate script, which is located in the
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environment's bin/ directory:
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source foobar/bin/activate
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This will change your $PATH so its first entry is the virtualenv’s bin/ directory.
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If you install a package in your virtual environment, you'll see that executable
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scripts are placed in foobar/bin/ and eggs in foobar/lib/python2.X/site-packages/
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easy_install yolk
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Yolk is a small command line tool which can, among other things, list the
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currently installed Python packages on your system:
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yolk -l
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Virtualenv inherits packages from the system's default site-packages directory.
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This is especially useful when relying on certain packages being available,
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so you don't have to go through installing them in every environment.
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To leave an environment, simply run deactivate:
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deactivate
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If you execute he yolk command now, you will see that it won't work because the
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package was installed only in your virtual environment.
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Once you reactivate your environment it will be available again.
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```
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##### 来源
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```py
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I used different sources to find information for this article:
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the official virtualenv [website](http://www.virtualenv.org/en/latest/index.html "virtualenv latest"), from Chris Scott "[A Primer on virtualenv](http://iamzed.com/2009/05/07/a-primer-on-virtualenv/ "a primer on virtualenv")" and
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from Arthur Koziel '[Working with virtualenv](http://www.arthurkoziel.com/2008/10/22/working-virtualenv/ "working-virtualenv")'
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```
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