pip: 一个现代的，通用的 Python 包管理工具。提供了对Python 包的查找、下载、安装、卸载的功能。
windows：自带pip，直接使用。
Linux：执行下面命令即可完成安装。
wget https://bootstrap.pypa.io/get-pip.py --no-check-certificate
python get-pip.py
Usage: pip [options]
查看版本：pip show package_name
更新pip：python -m pip install --upgrade pip
安装包：pip install package_name（Pytorch，Keras，TensorFlow，等等）
升级包：pip install --upgrade package_name 或者 pip install -U package_name
卸载包：pip uninstall package_name
查看已安装包：pip show --files package_name
查看哪些包需要升级：pip list --outdated
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# pip --help
Usage:
pip <command> [options]
Commands:
install Install packages. 安装包
download Download packages. 下载包
uninstall Uninstall packages. 卸载包
freeze Output installed packages in requirements format. 按着一定格式输出已安装包列表
list List installed packages. 列出已安装包
show Show information about installed packages. 显示包详细信息
check Verify installed packages have compatible dependencies.检查包的依赖关系是否完整
config Manage local and global configuration.管理配置
search Search PyPI for packages.搜索包
wheel Build wheels from your requirements.
hash Compute hashes of package archives.计算包的hash值
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