python使用pip卸载和安装库

pip

先来演示pip的错误打开方式：

C:\Users\86188>py
Python 3.8.2 (tags/v3.8.2:7b3ab59, Feb 25 2020, 22:45:29) [MSC v.1916 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> pip
Traceback (most recent call last):
  File "", line 1, in <module>
NameError: name 'pip' is not defined
>>>

问题出在哪呢？细心的同学会问了。其实呢，pip虽然是python的自带工具，而且安装了python之后会自动安装上pip，但pip工具并不能在python中打开哦！
下面我们演示如何在命令行中退出python，之后打开pip：

>>> exit()

C:\Users\86188>pip

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.
  cache                       Inspect and manage pip's wheel cache.
  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.
  --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 6000.0 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 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
  --no-python-version-warning
                              Silence deprecation warnings for upcoming unsupported Pythons.

C:\Users\86188>

先输入exit()，回车，我们就从python的界面退出了。
接着输入pip回车，就出现了长达一整页的提示，其中包括了install、uninstall等，都是可以使用pip完成的功能。
那么我们来用pip卸载一个库吧！首先，以绘图工具pandas为例来试一试：

C:\Users\86188>pip uninstall pandas
Found existing installation: pandas 1.0.5
Uninstalling pandas-1.0.5:
  Would remove:
    c:\users\86188\appdata\local\programs\python\python38-32\lib\site-packages\pandas-1.0.5.dist-info\*
    c:\users\86188\appdata\local\programs\python\python38-32\lib\site-packages\pandas\*
Proceed (y/n)? 

输入pip uninstall pandas，会看到命令行出现以上反应，并且会有一个”继续（是/否）的提示，此时如果我们输入y并按回车，卸载进程就会继续，如果我们输入n并按回车，卸载过程就会停止。
我输入了y和回车，结果如下：

 Proceed (y/n)? y
  Successfully uninstalled pandas-1.0.5

接下来我们再来安装，输入“pip install pandas"，可以看到如下界面：

C:\Users\86188>pip install pandas
Looking in indexes: http://pypi.douban.com/simple
Collecting pandas
  Downloading http://pypi.doubanio.com/packages/0d/3b/c306fc4c669f9208ba5a62d29a71fcb5df3be80a914da9e7b30ad682589f/pandas-1.0.5-cp38-cp38-win32.whl (7.6 MB)
     |████████████████████████████████| 7.6 MB 1.3 MB/s
Requirement already satisfied: numpy>=1.13.3 in c:\users\86188\appdata\local\programs\python\python38-32\lib\site-packages (from pandas) (1.19.0)
Requirement already satisfied: python-dateutil>=2.6.1 in c:\users\86188\appdata\roaming\python\python38\site-packages (from pandas) (2.8.1)
Requirement already satisfied: pytz>=2017.2 in c:\users\86188\appdata\local\programs\python\python38-32\lib\site-packages (from pandas) (2020.1)
Requirement already satisfied: six>=1.5 in c:\users\86188\appdata\roaming\python\python38\site-packages (from python-dateutil>=2.6.1->pandas) (1.14.0)
Installing collected packages: pandas
Successfully installed pandas-1.0.5

此时需要联网，进度条是下载的进度，Successfully installed pandas-1.0.5是”成功安装pandas-1.0.5版本“的意思。