第一次执行python -m pip，第二次执行pip。
pip不在PATH中，但python在。您可以解决这个问题，也可以使用python -m pip调用它。
也有可能您只需要刷新控制台窗口，这样它就可以接收您对PATH所做的更改。尝试关闭您的终端并重新打开它，看看您是否有同样的问题。

我尝试了行python -m pip，但写得像py -m pip，然后命令提示符显示：

Commands:
  install                     Install packages.
  download                    Download packages.
  uninstall                   Uninstall packages.
  freeze                      Output installed packages in requirements format.
  inspect                     Inspect the python environment.
  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.
  cache                       Inspect and manage pip's wheel cache.
  index                       Inspect information available from package indexes.
  wheel                       Build wheels from your requirements.
  hash                        Compute hashes of package archives.
  completion                  A helper command used for command completion.
  debug                       Show information useful for debugging.
  help                        Show help for commands.

General Options:
  -h, --help                  Show help.
  --debug                     Let unhandled exceptions propagate outside the main subroutine, instead of logging them
                              to stderr.
  --isolated                  Run pip in an isolated mode, ignoring environment variables and user configuration.
  --require-virtualenv        Allow pip to only run in a virtual environment; exit with an error otherwise.
  --python <python>           Run pip with the specified Python interpreter.
  -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.
  --no-input                  Disable prompting for input.
  --keyring-provider <keyring_provider>
                              Enable the credential lookup via the keyring library if user input is allowed. Specify
                              which mechanism to use [disabled, import, subprocess]. (default: disabled)
  --proxy <proxy>             Specify a proxy in the form scheme://[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 or host:port pair as trusted, even though it does not have valid or any
                              HTTPS.
  --cert <path>               Path to PEM-encoded CA certificate bundle. If provided, overrides the default. See 'SSL
                              Certificate Verification' in pip documentation for more information.
  --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.
  --no-python-version-warning
                              Silence deprecation warnings for upcoming unsupported Pythons.
  --use-feature <feature>     Enable new functionality, that may be backward incompatible.
  --use-deprecated <feature>  Enable deprecated functionality, that will be removed in the future.

我最初试图安装'pandas'包，所以我尝试了这个：Py -m pip install pandas成功了
我希望能帮上忙。