其实，pip就是 Python标准库（The Python Standard Library）中的一个包，这个包比较特殊，用它可以来管理Python标准库（The Python Standard Library）中其他的包。pip支持从PyPI（https://pypi.org/ ），版本控制，本地项目以及直接从分发文件进行安装。pip是一个命令行程序。 安装pip后，会向系统添加一个pip命令，该命令可以从命令提示符运行。
目前，pip 是The Python Packaging Authority (PyPA) 推荐的 Python 包管理工具！
The Python Packaging Authority (PyPA) is a working group that maintains many of the relevant projects in Python packaging.
pip安装从 Python 2 版本 >=2.7.9 或 Python 3 版本 >=3.4 开始，官网的安装包中已经自带了 pip，在安装时用户可以直接选择安装。或者如果使用由 virtualenv 或者 pyvenv 创建的 Virtual Environment，那么 pip 也是被默认安装的。
如果没有在安装python时候，选择上"安装pip"选项，那么也可以从本地安装。例如，直接使用get-pip.py进行安装。
首先从官网下载get-pip.py；
然后直接运行python get-pip.py即可；
pip使用安装后，在命令行中键入：pip+ 回车，就会出现如下使用说明：
Usage: pip[options] Commands: install Install packages. download Download packages. uninstall Uninstall packages. freeze Output installed packages in requirements format. list List installed packages. show Show information about installed packages. check Verify installed packages have compatible dependencies. config Manage local and global configuration. search Search PyPI for packages. wheel Build wheels from your requirements. hash Compute hashes of package archives. completion A helper command used for command completion. help Show help for commands. General Options: -h, --help Show help. --isolated Run pip in an isolated mode, ignoring environment variables and user configuration. -v, --verbose Give more output. Option is additive, and can be used up to 3 times. -V, --version Show version and exit. -q, --quiet Give less output. Option is additive, and can be used up to 3 times (corresponding to WARNING, ERROR, and CRITICAL logging levels). --log Path to a verbose appending log. --proxy Specify a proxy in the form [user:passwd@]proxy.server:port. --retries Maximum number of retries each connection should attempt (default 5 times). --timeout Set the socket timeout (default 15 seconds). --exists-action Default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup, (a)bort). --trusted-host Mark this host as trusted, even though it does not have valid or any HTTPS. --cert Path to alternate CA bundle. --client-cert Path to SSL client certificate, a single file containing the private key and the certificate in PEM format. --cache-dir Store the cache data in . --no-cache-dirDisable the cache. --disable-pip-version-check Don't periodically check PyPI to determine whether a new version of pip is available for download. Implied with --no-index. --no-color Suppress colored output
pip命令组合比较灵活，下面重点介绍几个。
install命令行直接键入pip install + 回车，则 出现如下提示：ERROR: You must give at least one requirement to install (see "pip help install")。接着我们键入pip help install,就会出现pip install的使用说明了，如下：
Usage: pip install [options][package-index-options] ... pip install [options] -r [package-index-options] ... pip install [options] [-e] ... pip install [options] [-e] ... pip install [options] ... Description: Install packages from: - PyPI (and other indexes) using requirement specifiers. - VCS project urls. - Local project directories. - Local or remote source archives. pip also supports installing from "requirements files", which provide an easy way to specify a whole environment to be installed. Install Options: -r, --requirement Install from the given requirements file. This option can be used multiple times. -c, --constraint Constrain versions using the given constraints file. This option can be used multiple times. --no-deps Don't install package dependencies. --pre Include pre-release and development versions. By default, pip only finds stable versions. -e, --editable Install a project in editable mode (i.e. setuptools "develop mode") from a local project path or a VCS url. -t, --target Install packages into . By default this will not replace existing files/folders in . Use --upgrade to replace existing packages in with new versions. --platform only use wheels compatible with . Defaults to the platform of the running system. --python-version only use wheels compatible with Python interpreter version . If not specified, then the current system interpreter minor version is used. A major version (e.g. '2') can be specified to match all minor revs of that major version. A minor version (e.g. '34') can also be specified. --implementation only use wheels compatible with Python implementation , e.g. 'pp', 'jy', 'cp', or 'ip'. If not specified, then the current interpreter implementation is used. Use 'py' to force implementation-agnostic wheels. --abi only use wheels compatible with Python abi , e.g. 'pypy_41'. If not specified, then the current interpreter abi tag is used. Generally you will need to specify --implementation, --platform, and --python-version when using this option. --user Install to the Python user install directory for your platform. Typically ~/.local/, or %APPDATA%Python on Windows. (See the Python documentation for site.USER_base for full details.) --root Install everything relative to this alternate root directory. --prefix Installation prefix where lib, bin and other top-level folders are placed -b, --build Directory to unpack packages into and build in. Note that an initial build still takes place in a temporary directory. The location of temporary directories can be controlled by setting the TMPDIR environment variable (TEMP on Windows) appropriately. When passed, build directories are not cleaned in case of failures. --src Directory to check out editable projects into. The default in a virtualenv is " /src". The default for global installs is " /src". -U, --upgrade Upgrade all specified packages to the newest available version. The handling of dependencies depends on the upgrade-strategy used. --upgrade-strategy Determines how dependency upgrading should be handled [default: only-if-needed]. "eager" - dependencies are upgraded regardless of whether the currently installed version satisfies the requirements of the upgraded package(s). "only-if-needed" - are upgraded only when they do not satisfy the requirements of the upgraded package(s). --force-reinstall Reinstall all packages even if they are already up-to-date. -I, --ignore-installed Ignore the installed packages (reinstalling instead). --ignore-requires-python Ignore the Requires-Python information. --no-build-isolation Disable isolation when building a modern source distribution. Build dependencies specified by PEP 518 must be already installed if this option is used. --install-option Extra arguments to be supplied to the setup.py install command (use like --install-option="-- install-scripts=/usr/local/bin"). Use multiple --install-option options to pass multiple options to setup.py install. If you are using an option with a directory path, be sure to use absolute path. --global-option Extra global options to be supplied to the setup.py call before the install command. --compile Compile Python source files to bytecode --no-compile Do not compile Python source files to bytecode --no-warn-script-location Do not warn when installing scripts outside PATH --no-warn-conflicts Do not warn about broken dependencies --no-binary Do not use binary packages. Can be supplied multiple times, and each time adds to the existing value. Accepts either :all: to disable all binary packages, :none: to empty the set, or one or more package names with commas between them. Note that some packages are tricky to compile and may fail to install when this option is used on them. --only-binary Do not use source packages. Can be supplied multiple times, and each time adds to the existing value. Accepts either :all: to disable all source packages, :none: to empty the set, or one or more package names with commas between them. Packages without binary distributions will fail to install when this option is used on them. --prefer-binaryPrefer older binary packages over newer source packages. --no-clean Don't clean up build directories. --require-hashes Require a hash to check each requirement against, for repeatable installs. This option is implied when any package in a requirements file has a --hash option. --progress-bar Specify type of progress to be displayed [off|on|ascii|pretty|emoji] (default: on) Package Index Options: -i, --index-url base URL of Python Package Index (default https://pypi.org/simple). This should point to a repository compliant with PEP 503 (the simple repository API) or a local directory laid out in the same format. --extra-index-url Extra URLs of package indexes to use in addition to --index-url. Should follow the same rules as --index-url. --no-index Ignore package index (only looking at --find-links URLs instead). -f, --find-links If a url or path to an html file, then parse for links to archives. If a local path or file:// url that's a directory, then look for archives in the directory listing. --process-dependency-links Enable the processing of dependency links. General Options: -h, --help Show help. --isolated Run pip in an isolated mode, ignoring environment variables and user configuration. -v, --verbose Give more output. Option is additive, and can be used up to 3 times. -V, --version Show version and exit. -q, --quiet Give less output. Option is additive, and can be used up to 3 times (corresponding to WARNING, ERROR, and CRITICAL logging levels). --log Path to a verbose appending log. --proxy Specify a proxy in the form [user:passwd@]proxy.server:port. --retries Maximum number of retries each connection should attempt (default 5 times). --timeout Set the socket timeout (default 15 seconds). --exists-action Default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup, (a)bort). --trusted-host Mark this host as trusted, even though it does not have valid or any HTTPS. --cert Path to alternate CA bundle. --client-cert Path to SSL client certificate, a single file containing the private key and the certificate in PEM format. --cache-dir Store the cache data in . --no-cache-dirDisable the cache. --disable-pip-version-check Don't periodically check PyPI to determine whether a new version of pip is available for download. Implied with --no-index. --no-color Suppress colored output
上面一大堆，总结来说，安装命令就是：pip install <包名> 或 pip install -r requirements.txt（对于本地安装包可以指定路径）。唯一需要特殊说明的是，安装时可以指定版本号来安装，举例如下：
pip install SomePackage# 最新版本 pip install SomePackage==1.0.4 # 指定版本 pip install 'SomePackage>=1.0.4' # 最小版本uninstall
卸载安装包命令：pip uninstall <包名> 或 pip uninstall -r requirements.txt
升级包pip install -U <包名> 或：pip install <包名> --upgrade
freezepip freeze,查看已经安装的包及版本信息。导出到指定文件中，如图，注意 “ > ”，文件名称随意。常见按第二种写法。
list列出当前已经安装的包。使用命令pip list -o则可查询可升级的包。
show显示包所在目录及信息，格式为：pip show <包名>。如果不加包名，则提示ERROR: Please provide a package name or names.。
search搜索包，格式为：pip search <搜索关键字>。如果不写关键字，则提示ERROR: Missing required argument (search query).。
更多关于pip安装及使用方法请查看下面的相关链接
