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pip 是啥

  pip 是 Python 的包安装程序。其实，pip 就是 Python 标准库（The Python Standard Library）中的一个包，只是这个包比较特殊，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，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！英文比较好的同学可以直接去官网参看其用户手册

PyPI（The Python Package Index，Python包索引）是 Python 编程语言的软件存储库。通常，我们就是从这上面安装各种 Python 的包，也可以在上面发布自己的包。
The Python Packaging Authority (PyPA) is a working group that maintains many of the relevant projects in Python packaging.

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。
  如果没有在安装的时候，选择上安装pip，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。

更详细的安装，可以直接去官网参看安装说明

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 <command> [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>                Path to a verbose appending log.
  --proxy <proxy>             Specify a proxy in the form [user:passwd@]proxy.server:port.
  --retries <retries>         Maximum number of retries each connection should attempt (default 5 times).
  --timeout <sec>             Set the socket timeout (default 15 seconds).
  --exists-action <action>    Default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup,
                              (a)bort).
  --trusted-host <hostname>   Mark this host as trusted, even though it does not have valid or any HTTPS.
  --cert <path>               Path to alternate CA bundle.
  --client-cert <path>        Path to SSL client certificate, a single file containing the private key and the
                              certificate in PEM format.
  --cache-dir <dir>           Store the cache data in <dir>.
  --no-cache-dir              Disable 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] <requirement specifier> [package-index-options] ...
pip install [options] -r <requirements file> [package-index-options] ...
pip install [options] [-e] <vcs project url> ...
pip install [options] [-e] <local project path> ...
pip install [options] <archive url/path> ...
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 <file>    Install from the given requirements file. This option can be used multiple times.
-c, --constraint <file>     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 <path/url>   Install a project in editable mode (i.e. setuptools "develop mode") from a local project path or a
VCS url.
-t, --target <dir>          Install packages into <dir>. By default this will not replace existing files/folders in <dir>. Use
--upgrade to replace existing packages in <dir> with new versions.
--platform <platform>       Only use wheels compatible with <platform>. Defaults to the platform of the running system.
--python-version <python_version>
Only use wheels compatible with Python interpreter version <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 <implementation>
Only use wheels compatible with Python implementation <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 <abi>                 Only use wheels compatible with Python abi <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 <dir>                Install everything relative to this alternate root directory.
--prefix <dir>              Installation prefix where lib, bin and other top-level folders are placed
-b, --build <dir>           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 <dir>                 Directory to check out editable projects into. The default in a virtualenv is "<venv path>/src".
The default for global installs is "<current dir>/src".
-U, --upgrade               Upgrade all specified packages to the newest available version. The handling of dependencies
depends on the upgrade-strategy used.
--upgrade-strategy <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 <options>  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 <options>   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 <format_control>
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 <format_control>
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-binary             Prefer 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 <progress_bar>
Specify type of progress to be displayed [off|on|ascii|pretty|emoji] (default: on)
Package Index Options:
-i, --index-url <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 <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 <url>      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>                Path to a verbose appending log.
--proxy <proxy>             Specify a proxy in the form [user:passwd@]proxy.server:port.
--retries <retries>         Maximum number of retries each connection should attempt (default 5 times).
--timeout <sec>             Set the socket timeout (default 15 seconds).
--exists-action <action>    Default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup, (a)bort).
--trusted-host <hostname>   Mark this host as trusted, even though it does not have valid or any HTTPS.
--cert <path>               Path to alternate CA bundle.
--client-cert <path>        Path to SSL client certificate, a single file containing the private key and the certificate in
PEM format.
--cache-dir <dir>           Store the cache data in <dir>.
--no-cache-dir              Disable 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

freeze

pip freeze 查看已经安装的包及版本信息。导出到指定文件中。例如，pip freeze > requirements.txt，文件名称随意；也可以使用 pip install -r requirements.txt，两者等效。

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).。

参考

https://pip.pypa.io/en/stable/user_guide/