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你可以使用一个名为 pip 的程序来安装、升级和移除软件包。默认情况下 pip 将从 python package index <https://pypi.org> 安装软件包。你可以在浏览器中访问 python package index 或是使用 pip 受限的搜索功能:
(tutorial-env) $ pip search astronomy skyfield - elegant astronomy for python gary - galactic astronomy and gravitational dynamics. novas - the united states naval observatory novas astronomy library astroobs - provides astronomy ephemeris to plan telescope observations pyastronomy - a collection of astronomy related tools for python. ...
pip 有许多子命令：“search”、“install”、“uninstall”、“freeze”等等。（请参阅 指南以了解 pip 的完整文档。）
您可以通过指定包的名称来安装最新版本的包：
(tutorial-env) $ pip install novas collecting novas downloading novas-3.1.1.3.tar.gz (136kb) installing collected packages: novas running setup.py install for novas successfully installed novas-3.1.1.3
您还可以通过提供包名称后跟 == 和版本号来安装特定版本的包：
(tutorial-env) $ pip install requests==2.6.0 collecting requests==2.6.0 using cached requests-2.6.0-py2.py3-none-any.whl installing collected packages: requests successfully installed requests-2.6.0
如果你重新运行这个命令，pip 会注意到已经安装了所请求的版本并且什么都不做。您可以提供不同的版本号来获取该版本，或者您可以运行 pip install --upgrade 将软件包升级到最新版本：
我要评论(tutorial-env) $ pip install --upgrade requests
collecting requests
installing collected packages: requests
found existing installation: requests 2.6.0
uninstalling requests-2.6.0:
successfully uninstalled requests-2.6.0
successfully installed requests-2.7.0
pip uninstall 后跟一个或多个包名称将从虚拟环境中删除包。
pip show 将显示有关特定包的信息：
(tutorial-env) $ pip show requests --- metadata-version: 2.0 name: requests version: 2.7.0 summary: python http for humans. home-page: http://python-requests.org author: kenneth reitz author-email: me@kennethreitz.com license: apache 2.0 location: /users/akuchling/envs/tutorial-env/lib/python3.4/site-packages requires:
pip list 将显示虚拟环境中安装的所有软件包：
(tutorial-env) $ pip list novas (3.1.1.3) numpy (1.9.2) pip (7.0.3) requests (2.7.0) setuptools (16.0)
pip freeze` 将生成一个类似的已安装包列表，但输出使用 pip install 期望的格式。一个常见的约定是将此列表放在 requirements.txt 文件中：
(tutorial-env) $ pip freeze > requirements.txt (tutorial-env) $ cat requirements.txt novas==3.1.1.3 numpy==1.9.2 requests==2.7.0
然后可以将 requirements.txt 提交给版本控制并作为应用程序的一部分提供。然后用户可以使用 install -r 安装所有必需的包：
(tutorial-env) $ pip install -r requirements.txt collecting novas==3.1.1.3 (from -r requirements.txt (line 1)) ... collecting numpy==1.9.2 (from -r requirements.txt (line 2)) ... collecting requests==2.7.0 (from -r requirements.txt (line 3)) ... installing collected packages: novas, numpy, requests running setup.py install for novas successfully installed novas-3.1.1.3 numpy-1.9.2 requests-2.7.0
pip 有更多选择。有关 pip 的完整文档， 请参阅python教程。
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