为什么“pip help”没有列出 --upgrade？

Question

pip3 的关键选项之一是--upgrade. 那为什么不pip3 help描述呢？

1. 进行网络搜索以了解如何使用 pip3 升级 Python 3 包。有大量的答案，包括但不限于如何更新 Python 包？，所有的一般形式：

   sudo pip install [package_name] --upgrade

   观察该命令行中是否存在该选项--upgrade。

2. 输入pip3 help 响应：

Usage:   
  pip3 <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

请注意，该单词upgrade不在该选项列表中。

只想确认一下：

3. 类型pip3 help | grep upgrade。结果：

   找到零次出现。

可能有一个--upgrade被排除在 pip3 之外的原因help。

那是什么原因呢？

Answer 1

它列在pip install --help：

$ pip install --help | grep upgrade
                              <dir>. Use --upgrade to replace existing
  -U, --upgrade               Upgrade all specified packages to the newest
                              depends on the upgrade-strategy used.
  --upgrade-strategy <upgrade_strategy>
                              dependencies are upgraded regardless of whether
                              requirements of the upgraded package(s). "only-
                              if-needed" -  are upgraded only when they do not
                              satisfy the requirements of the upgraded

下面的标志pip --help是常规选项。