记录一个Django相关的异常（mysqlclient老生常谈）

异常是关于mysqlclient和PyMySQL的

这个异常有些老生常谈了，但是至今都是一个问题，尤其是Python3在不同系统上的兼容性相差较大。这次记录的版本是Python3.10（Python3.11），在Windows11系统版本上可以直接安装mysqlclient

我印象已经有很长一段时间，可以在Django中使用PyMySQL替代mysqlclient，并且这些年mysqlclient有各种依赖问题导致安装失败，相反PyMySQL则可以直接安装。

但是目前发现最新的Django5+Python3.11版本在Windows上正常安装mysqlclient了，且使用PyMySQL则导致一些不兼容的安装问题。而ubuntu22.04容器中的同版本Python就出现了下面的报错：
```
Collecting mysqlclient==2.2.4
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/79/33/996dc0ba3f03e2399adc91a7de1f61cb14b57ebdb4cc6eca8a78723043cb/mysqlclient-2.2.4.tar.gz (90 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error
  
  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [27 lines of output]
      /bin/sh: 1: pkg-config: not found
      /bin/sh: 1: pkg-config: not found
      /bin/sh: 1: pkg-config: not found
      Trying pkg-config --exists mysqlclient
      Command 'pkg-config --exists mysqlclient' returned non-zero exit status 127.
      Trying pkg-config --exists mariadb
      Command 'pkg-config --exists mariadb' returned non-zero exit status 127.
      Trying pkg-config --exists libmariadb
      Command 'pkg-config --exists libmariadb' returned non-zero exit status 127.
      Traceback (most recent call last):
        File "/home/env/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 363, in <module>
          main()
        File "/home/env/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 345, in main
          json_out['return_val'] = hook(**hook_input['kwargs'])
        File "/home/env/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 130, in get_requires_for_build_wheel
          return hook(config_settings)
        File "/tmp/pip-build-env-wrm_4di5/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 325, in get_requires_for_build_wheel
          return self._get_build_requires(config_settings, requirements=['wheel'])
        File "/tmp/pip-build-env-wrm_4di5/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 295, in _get_build_requires
          self.run_setup()
        File "/tmp/pip-build-env-wrm_4di5/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 311, in run_setup
          exec(code, locals())
        File "<string>", line 155, in <module>
        File "<string>", line 49, in get_config_posix
        File "<string>", line 28, in find_package_name
      Exception: Can not find valid pkg-config name.
      Specify MYSQLCLIENT_CFLAGS and MYSQLCLIENT_LDFLAGS env vars manually
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: subprocess-exited-with-error

× Getting requirements to build wheel did not run successfully.
│ exit code: 1
╰─> See above for output.

note: This error originates from a subprocess, and is likely not a problem with pip.
```

依据异常提示，这个错误提示是由于缺少 pkg-config 工具导致的。pkg-config 是一个帮助定位编译器和链接器标志的工具，某些 Python 包需要它来定位依赖库的位置。

这里推荐先后安装以下两个包：
```shell
apt install pkg-config
```

另外，安装mysql-client时，libmysqlclient-dev 是 MySQL 客户端库的开发包，通常用于构建需要连接到 MySQL 的软件。在大多数情况下，需要构建 Python 的 MySQL 客户端库（如 mysqlclient），您需要安装 libmysqlclient-dev。

```shell
apt install libmysqlclient-dev
```