环境：Python 3.8.5
在使用pymysql去数据库查询数据时，出现了如下错误：
Exception ignored in: <function MysqlPoolClient.__del__ at 0x000001107810DC10>Traceback (most recent call last):File "E:\test\work\myspider\utils\mysql_pool.py", line 39, in __del__self.dispose()File "E:\test\work\myspider\utils\mysql_pool.py", line 206, in disposeself.end('commit')File "E:\test\work\myspider\utils\mysql_pool.py", line 196, in mit()File "E:\test\venv1\lib\site-packages\dbutils\steady_db.py", line 435, in commitraise error # re-raise the original errorFile "E:\test\venv1\lib\site-packages\dbutils\steady_db.py", line 426, in mit()File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 422, in commitself._read_ok_packet()File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 396, in _read_ok_packetpkt = self._read_packet()File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 658, in _read_packetraise err.InternalError(pymysql.err.InternalError: Packet sequence number wrong - got 5 expected 1
最开始查找的相关资料，都是说多线程未加锁导致类似问题的出现，例如：python pymysql 多线程 读写数据库 报错 Packet sequence number wrong
但实际上，mysql_pool.py是基于pymysql封装的模块，已经注意了多线程锁的问题，所以考虑实际问题不是因为未加锁。
重新使用traceback模块打印异常，发现了如下错误：
Traceback (most recent call last):File "E:/test/work/myspider/spider_files/tianyancha_new/mysql_to_es.py", line 52, in get_one_from_companyresult = client.getOne(sql)File "E:\test\work\myspider\utils\mysql_pool.py", line 88, in getOnecount = self._cursor.execute(sql)File "E:\test\venv1\lib\site-packages\dbutils\steady_db.py", line 598, in tough_methodresult = method(*args, **kwargs) # try to executeFile "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\cursors.py", line 163, in executeresult = self._query(query)File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\cursors.py", line 321, in _queryconn.query(q)File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 505, in queryself._affected_rows = self._read_query_result(unbuffered=unbuffered)File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 724, in _read_query_resultresult.read()File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 1076, in readself._read_result_packet(first_packet)File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 1146, in _read_result_packetself._read_rowdata_packet()File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 1184, in _read_rowdata_packetrows.append(self._read_row_from_packet(packet))File "C:\Users\admin\AppData\Roaming\Python\Python38\site-packages\pymysql\connections.py", line 1203, in _read_row_from_packetdata = converter(data)TypeError: conversion from bytes to Decimal is not supported
看见“Decimal”想起来，要查询的数据中，有个字段是Decimal类型，然后继续查找相关资料：
pymysql TypeError: conversion from bytes to Decimal is not supported，这位大佬直接去把pymysql源码做了修改，应该也能解决问题（未实验）
后来参考了这个：python-Django錯誤：不支持從字節到十進位的轉換，大体意思是，由于use_unicode设置为False导致。
use_unicode是连接mysql时设置的一个参数，在python3中，该参数默认是True，但是在封装的mysql_pool.py中，use_unicode设置的为False，所以产生了上面的错误。重新将use_unicode改为True，即可避免上述问题的出现了。
参考：PyMySQL 官方文档
另外，当use_unicode设置为False时，查询结果里的文本对象都是字节类型；设置为True后，获取到的文本对象是字符串类型的数据。
