Python类抛出:无法将'list‘对象转换为str隐含

Question

似乎我无法访问Python3.5中的字段Database.query_stmt_list[i]。

我的代码看起来像：

class Database():
    query_stmt_list = ['SELECT','INSERT','UPDATE','DELETE','FROM','WHERE']
    def __init__(self):
        self.query_stmt_list = Database.query_stmt_list
    def db_select(self, *selected_fields, **kwargs):
        self.selected_fields = selected_fields = list(selected_fields)
        self.table = (kwargs['table']
                      if 'table' in kwargs 
                      else selected_fields.pop())
        self.where_field = (kwargs['where_field']
                            if 'where_field' in kwargs
                            else selected_fields.pop())
        try:
            with self.db.cursor() as cursor:
                sql_tld_id_query = Database.query_stmt_list[0]+ selected_fields + Database.query_stmt_list[4] + table + Database.query_stmt_list[5] + where_field + '=' + 'www.website.com'
            print("sql_tld_id_query is {}".format(sql_tld_id_query))   
        except Exception as gatherid_err:
            print("exception was {}".format(gatherid_err))
            self.db.rollback()

#instantiate class/method       
dbclass = Database()
dbclass.set_db_setting('localhost', 'root', 'password', 'garbagedb')
dbclass.db_select(['id', 'name'], table='tld', where_field='name')

我犯了一个错误，比如：

无法将“list”对象隐式转换为str

在线：

sql_tld_id_query = Database.query_stmt_list[0]+ selected_fields + Database.query_stmt_list[4] + table + Database.query_stmt_list[5] + where_field + '=' + 'www.website.com'

全栈

$ python dbcrud.py 
connected to: garbagedb
exception was sequence item 0: expected str instance, list found

我在这里做错什么了？有人看到出什么问题了吗？

谢谢

Answer 1

你想在那条线上形成一个字符串。而不是这个词

selected_fields

它是一个列表，而不是字符串，似乎是你想要的

', '.join(selected_fields)

要形成一个正确的逗号分隔，符合SQL的字段列表，是吗？

sql_tld_id_query = Database.query_stmt_list[0]+ ', '.join(selected_fields) + Database.query_stmt_list[4] + table + Database.query_stmt_list[5] + where_field + '=' + 'www.website.com'