如果使用代码：

def insert_into_db(dbcursor, table, *cols,**vals):
    query = "INSERT INTO {} ({}) VALUES ({})".format(table,",".join(cols), ",".join(vals))
    print(query)

insert_into_db('cursor_here', 'table_here', 'name', 'city', name_person='diego', city_person='Sao Paulo')

python返回：

INSERT INTO table_here (name,city) VALUES (name_person,city_person)

另一方面：

def new_insert_into_db(dbcursor, table, *cols,**vals):
    vals2 = ''
    for first_part, second_part in vals.items():
        vals2 += '\'' + second_part + '\','
    vals2 = vals2[:-1]
    query = "INSERT INTO {} ({}) VALUES ({})".format(table,",".join(cols), vals2)
    print(query)

new_insert_into_db('cursor_here', 'table_here', 'name', 'city', name_person='diego', city_person='Sao Paulo')

python将返回正确的sql:

INSERT INTO table_here (name,city) VALUES ('diego','Sao Paulo')

您应该打印您生成的sql语句，这样可以更容易地看到错误所在。
但我想你需要报价 ' 关于字符串值 ",".join(vals) （如果有字符串值。
所以你的代码产生了

insert into test (path,) values (test.com/test2,);

但它应该产生

insert into test (`path`) values ('test.com/test2');

否则试试看https://github.com/markuman/mariasql/ 这使得使用pymysql向mariadb/mysql插入数据非常容易。

通常在python中，将参数化查询传递给db驱动程序。参见pymysql文档中的这个例子；它构建了 INSERT 使用占位符进行查询，然后调用 cursor.execute() 传递查询和实际值的元组。
出于安全目的，还建议使用参数化查询，因为它可以抵御许多常见的sql注入攻击。

更改您的查询如下

query = "INSERT INTO {} ({}) VALUES ('{}')".format(table, ",".join(cols),  "'),('".join(vals))

在使用join时，变量应该是列表而不是字符串

table = 'test'
cols = ['path']
vals = ['test.com/test2', 'another.com/anothertest']

print(query)

"INSERT INTO test (path) VALUES ('test.com/test2'),('another.com/anothertest')"

更新：

def insert_into_db(dbconnection=None, table='', cols=None, vals=None):
    mycursor = dbconnection.cursor()
    if not (dbconnection and table and cols and vals):
        print('Must need all values')
        quit()
    try:
        query = "INSERT INTO {} ({}) VALUES ('{}')".format(table, ",".join(cols),  "'),('".join(vals))
        mycursor.execute(query)
        dbconnection.commit()
        print("inserted!")
    except pymysql.Error as exc:
        print("error inserting...\n {}".format(exc))

connection=conn_db()        

insertstmt=insert_into_db(dbconnection=connection, table='test', cols=['path'], vals=['test.com/test2'])