使用类而不在python中调用构造函数

Question

我有简单的类可以从数据库中获取查询。

# myClass.py
class DB:
    def __init__ (self, host, user, password):
        self.conn = MySQLdb.connect("localhost","****","****","***")
        self.conn.set_character_set('utf8mb4')
        cursor = self.conn.cursor()
        cursor.execute('SET NAMES utf8mb4;')
        cursor.execute('SET CHARACTER SET utf8mb4;')
        cursor.execute('SET character_set_connection=utf8mb4;')
    def query(self, q):
            cursor = self.conn.cursor()
            cursor.execute(q)
            return cursor

如果我使用下面的查询可以正常工作，

from myClass import DB
q = DB("..", "..", "..", "..")
_fetch = q.query("... ")

但是，如果由于我要声明第二行而希望摆脱第二行，请在myClass.py中传递host ..

所以，当我尝试

from myClass import DB
_fetch = DB.query("... ")

即使删除self,关键字，它也不允许我连接

Answer 1

您可以尝试类似：

# myClass.py

# code will be executed only once a the first import 
conn = MySQLdb.connect("localhost","****","****","***")
conn.set_character_set('utf8mb4')
cursor = conn.cursor()    
cursor.execute('SET NAMES utf8mb4;')
cursor.execute('SET CHARACTER SET utf8mb4;')
cursor.execute('SET character_set_connection=utf8mb4;')

class DB:
    # class attribute shared among all DB instance
    cursor = conn.cursor()
    # class method
    @classmethod
    def query(cls, q):
        cls.cursor.execute(q)
        return cursor

Answer 2

您可以创建类对象，然后导入并使用它：

# myClass.py
class DB:
    def __init__ (self, host, user, password):
        # ...

db = DB("..", "..", "..", "..")  # Create object ones.

其他模块中的某处：

from myClass import db

db.query("... ")