也许你可以使用重试包。

pip install retry
from sqlalchemy import exc

@retry(exc.OperationError, delay=5, tries=5)
def fun_name():
    try:
        #body of function
    except exc.OperationError:
        raise

当操作出错时，将重试5次，延时5秒

当服务器无法获取对表或数据库的处理操作的锁时，会发生这种情况，请尝试按照异常中的建议重新启动事务：

session_delete_mapping = Session()
session_delete_user= Session()
if request.method == "POST":
    user_id = request.form['user_list']
    try :
        num_rows_deleted_map = session_delete_mapping.query(UserRoleMapping).filter(UserRoleMapping.user_id == user_id).delete()
        num_rows_deleted_user = session_delete_user.query(UserRoleMapping).filter(User.id == user_id).delete()
        session_delete_mapping.commit()
        session_delete_user.commit()
        User.query.filter(User.id == user_id).delete()
        flash("Successfully deleted !!")
    except InternalError as e:
        # mysql error code of 'lock timeout'
        if e.orig[0] == 1205:
            # call this handler again with same arguments
        else:
            flash("Oops something went wrong : "+ str(e))
            session_delete_mapping.rollback()
            session_delete_user.rollback()
    except Exception as e:
        flash("Oops something went wrong : "+ str(e))
        session_delete_mapping.rollback()
        session_delete_user.rollback()
return render_template('index.html')

在捕获from sqlalchemy.exc import InternalError时不要忘记导入异常类
通常情况下，你很少会遇到这种异常，但如果没有，你应该检查你的服务器是否有巨大的或“停滞”的查询，并优化它们。而粗你可以增加wait_timeout在myslq配置文件。