Python上下文管理器

在python脚本工具中，配合with使用上下文管理器的写法将会非常nice，比如进行数据库操作，邮件发送等等一些具有连接、关闭的操作时。

• 第一种函数的写法

"""以发送邮件为例"""
import smtplib
from contextlib import contextmanager

SMTP_SERVER = ""
ACCOUNT = ""
PASSWORD = ""

@contextmanager
def connect():
    smtp_obj = smtplib.SMTP(SMTP_SERVER)
    smtp_obj.login(ACCOUNT, PASSWORD)
    yield smtp_obj
    smtp_obj.quit()

• 第二种类的写法

"""以连接数据库为例"""
import pymysql
import pymysql.cursors
from collections import namedtuple

DBConfig = namedtuple(
    "DBConfig",
    ['ip', 'user', 'pwd', 'port'],
    defaults=["127.0.0.1", "", "", 0]
)
DBMap = {...}


class Connect:

    def __init__(self, key, dbname):
        self.cfg = DBMap[key]
        self.dbname = dbname

    def __enter__(self):
        self.conn = pymysql.connect(
            host=self.cfg.ip,
            user=self.cfg.user,
            password=self.cfg.pwd,
            database=self.dbname,
            port=self.cfg.port,
        )
        self.cursor = self.conn.cursor(cursor=pymysql.cursors.DictCursor)
        return self.cursor

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.cursor.close()
        self.conn.close()


class ConnectAndCommit(Connect):

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.conn.commit()
        self.cursor.close()
        self.conn.close()