pip是什么？

pip 是 Python 标准库管理器，也就是一个工具让你安装不同的类库来使用。

当你要安装某些类库时，都会使用 pip，那 pip 除了安装类库之外，还能做什么呢？

首先，我们进入 cmd终端，输入 pip，查看当前 pip 的命令集合。

$ pipUsage: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.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 themain subroutine, instead of logging them tostderr.--isolated                  Run pip in an isolated mode, ignoring environmentvariables and user configuration.--require-virtualenv        Allow pip to only run in a virtual environment;exit with an error otherwise.-v, --verbose               Give more output. Option is additive, and can beused up to 3 times.-V, --version               Show version and exit.-q, --quiet                 Give less output. Option is additive, and can beused 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.--proxy <proxy>             Specify a proxy in the form[user:passwd@]proxy.server:port.--retries <retries>         Maximum number of retries each connection shouldattempt (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, eventhough it does not have valid or any HTTPS.--cert <path>               Path to PEM-encoded CA certificate bundle. Ifprovided, overrides the default. See 'SSLCertificate Verification' in pip documentationfor more information.--client-cert <path>        Path to SSL client certificate, a single filecontaining the private key and the certificate inPEM format.--cache-dir <dir>           Store the cache data in <dir>.--no-cache-dir              Disable the cache.--disable-pip-version-checkDon't periodically check PyPI to determinewhether a new version of pip is available fordownload. Implied with --no-index.--no-color                  Suppress colored output.--no-python-version-warningSilence deprecation warnings for upcomingunsupported Pythons.--use-feature <feature>     Enable new functionality, that may be backwardincompatible.--use-deprecated <feature>  Enable deprecated functionality, that will beremoved in the future.

pip --version

只要在终端输入 pip --version 或者 pip -V 就能得到当前系统安装的 pip 版本，同时也会知道对应的 Python 版本。

$ pip --version
pip 22.0.4 from /Users/niuben/opt/anaconda3/lib/python3.9/site-packages/pip (python 3.9)$ pip -V
pip 22.0.4 from /Users/niuben/opt/anaconda3/lib/python3.9/site-packages/pip (python 3.9)

pip list 查询当前已安装类库

$ pip list
Package                            Version
---------------------------------- --------------------
alabaster                          0.7.12
anaconda-client                    1.9.0
anaconda-navigator                 2.1.1
anaconda-project                   0.10.1
anyio                              2.2.0
appdirs                            1.4.4
applaunchservices                  0.2.1
appnope                            0.1.2
appscript                          1.1.2
argh                               0.26.2
argon2-cffi                        20.1.0
arrow                              0.13.1
asn1crypto                         1.4.0
astroid                            2.6.6
astropy                            4.3.1
async-generator                    1.10
atomicwrites                       1.4.0
attrs                              21.2.0
autopep8                           1.5.7
Babel                              2.9.1

在安装包之前，先看一下这个包否已安装，或者当前包的版本，使用如下命令:

pip list -o

pip install 安装类库

默认情况下 pip 使用的是国外的镜像，在下载的时候速度非常慢，下载速度是几kb或者几十kb，花费的时间比较长，请移步查看 python 更新pip镜像源
安装类库时，只需要使用 pip install --upgrade 包名称 就可以安装对应的类库了

如果没有对应的类库，就会安装失败，提示找不到

$ pip install --upgrade zipp     # 由于已经安装，会提示已安装并说明类库安装位置
Looking in indexes: https://mirrors.aliyun.com/pypi/simple/
Requirement already satisfied: zipp in ./opt/anaconda3/lib/python3.9/site-packages (3.6.0)$ pip install --upgrade zip111     # 输入错误的包名，会提示错误，找不到
Looking in indexes: https://mirrors.aliyun.com/pypi/simple/
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', timeout('_ssl.c:1112: The handshake operation timed out'))': /pypi/simple/zipp111/
WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', timeout('_ssl.c:1112: The handshake operation timed out'))': /pypi/simple/zipp111/
ERROR: Could not find a version that satisfies the requirement zipp111 (from versions: none)
ERROR: No matching distribution found for zipp111

有时候我们需要安装指定版本的类库，新版本有时候会出现一些兼容问题，导致冲突

这时候安装类库包时，可以使用 pip install --upgrade 包名称==版本号 指定版本号

$ pip install --upgrade zipp==3.6.0
Looking in indexes: https://mirrors.aliyun.com/pypi/simple/
Collecting zipp==3.6.0Downloading https://mirrors.aliyun.com/pypi/packages/bd/df/d4a4974a3e3957fd1c1fa3082366d7fff6e428ddb55f074bf64876f8e8ad/zipp-3.6.0-py3-none-any.whl (5.3 kB)
Installing collected packages: zippAttempting uninstall: zippFound existing installation: zipp 3.8.0Uninstalling zipp-3.8.0:Successfully uninstalled zipp-3.8.0
Successfully installed zipp-3.6.0

有时候安装完类库时，会提示你升级 pip，当然升级下最好啦

python3 -m pip install –upgrade pip => 升級 pip 套件

pip show 了解指定类库资讯

使用 pip show <包名> ，可以更加详细了解类库相关说明

pip show Babel
Name: Babel
Version: 2.9.1
Summary: Internationalization utilities
Home-page: http://babel.pocoo.org/
Author: Armin Ronacher
Author-email: armin.ronacher@active-4.com
License: BSD
Location: /Users/niuben/opt/anaconda3/lib/python3.9/site-packages
Requires: pytz
Required-by: jupyterlab-server, Sphinx

pip uninstall 卸载类库

当你不需要这个类库或者觉得太占空间时，可以使用 pip uninstall <类库名> ，卸载对应的类库

在删除的时候，会询问你一次，是否确定删除

如果真的删除了，需要时，可以再通过 pip install <类库名> 安装回来

$ pip uninstall zipp
Found existing installation: zipp 3.6.0
Uninstalling zipp-3.6.0:Would remove:/Users/niuben/opt/anaconda3/lib/python3.9/site-packages/zipp-3.6.0.dist-info/*/Users/niuben/opt/anaconda3/lib/python3.9/site-packages/zipp.py
Proceed (Y/n)? ySuccessfully uninstalled zipp-3.6.0$ pip install zipp
Looking in indexes: https://mirrors.aliyun.com/pypi/simple/
Collecting zippDownloading https://mirrors.aliyun.com/pypi/packages/80/0e/16a7ee38617aab6a624e95948d314097cc2669edae9b02ded53309941cfc/zipp-3.8.0-py3-none-any.whl (5.4 kB)
Installing collected packages: zipp
Successfully installed zipp-3.8.0

pip freeze 列出所有安装类库

pip list 不就能列出所有安装的类库吗？那为什么还有 pip freeze 呢？

pip list 列出的是所有安装的类库包，可并不是所有的类库包都可以删除的，例如：pip、setuptools等等

它们就像是手机中预载的系统app，没有办法删除，而通过 pip freeze 可以取出自己安装过的类库包

当然如果一定要用 pip freeze 来显示所有包，可以加上参数 --all ，就可以啦

pip freeze > requirements.txt 将本地安装包导出写入文本

当我们换电脑或者使用新的系统来跑当前 Python 相同的代码时，可以一键安装对应的类库，以及轻松搞定类库版本问题

换系统时，有时候会因为某些类库或者版本问题，造成冲突或者异常，不如直接导出到 txt 文本中，再通过安装的方式，快速复制一套 Python 开发环境，省时又省力。

$ pip freeze > requirements.txt  # 把电脑的已安装的类库包，导出到 requirements.txt
$ cat requirements.txt  # 查看 requirements.txts 內容
cat requirements.txt
alabaster @ file:///home/ktietz/src/ci/alabaster_1611921544520/work
anaconda-client @ file:///opt/concourse/worker/volumes/live/866d4dd0-ff5b-4d0b-718d-0267a3b10e06/volume/anaconda-client_1635342573767/work
anaconda-navigator==2.1.1
anaconda-project @ file:///tmp/build/80754af9/anaconda-project_1626085644852/work
anyio @ file:///opt/concourse/worker/volumes/live/96440bbe-d2f1-4a9e-5edf-600248ff38bd/volume/anyio_1617783321037/work/dist
appdirs==1.4.4
applaunchservices @ file:///Users/ktietz/demo/mc3/conda-bld/applaunchservices_1630511705208/work
appnope @ file:///opt/concourse/worker/volumes/live/6ca6f098-d773-4461-5c91-a24a17435bda/volume/appnope_1606859448531/work
appscript @ file:///opt/concourse/worker/volumes/live/00049ed6-6263-4a6e-72b9-9d990f6e2f07/volume/appscript_1611427000595/work
argh==0.26.2
argon2-cffi @ file:///opt/concourse/worker/volumes/live/38e8fb2b-1295-4bdf-4adf-b20acbe4d91b/volume/argon2-cffi_1607022498041/work
arrow @ file:///opt/concourse/worker/volumes/live/1c202787-83f7-4b70-6d98-b40769f597f4/volume/arrow_1617737667847/work
asn1crypto @ file:///tmp/build/80754af9/asn1crypto_1596577642040/work
...

这时候在另一套新系统终端上执行 pip install -r requirements.txt，就能快速将旧系统原有的类库安装到新系统上了。

pip install -r requirements.txt

pip 整理本地安装类库

可以先执行 pip freeze > requirements.txt 导出所有已安装类库包，然后再修改 requirements.txt，将需要删除的类库保留，然后执行 pip uninstall -r requirements.txt 就能快速删除指定的类库了，如果需要恢复，再执行pip install -r requirements.txt 即可。