python中with语句结合上下文管理器操作详解

# 1. 导入模块
import pymysql

# 创建自定义上下文管理器对象
class MyDatabase(object):
 # 接收参数并创建数据库连接对象
 def __init__(self, host, port, user, passwd, database):
  self.__db = pymysql.Connection(host, port, user, passwd, database, charset='utf8')

 # 返回数据库连接对象
 def __enter__(self):
  return self.__db

 # 关闭数据库连接
 def __exit__(self, exc_type, exc_val, exc_tb):
  self.__db.close()


def main():
 # 使用with关键字接收enter返回的对象给db
 with MyDatabase('localhost', 3306, 'root', 'mysql', 'JDDB') as db:
  # 利用db创建游标
  cur = db.cursor()
  sql = '''select * from %s'''
  cur.execute(sql, (goods,))
  result = cur.fetchall()
  for i in result:
   print(i)
  # 关闭游标
  cur.close()

# 程序入口
if __name__ == '__main__':
 main()

# 1.导入socket模块
import socket


class MySocket(object):
 # 2.编写init方法接收port参数
 def __init__(self, port):
  self.__port = port
  # 3.创建socket对象
  self.__sk = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

 # 4.编写enter方法返回套接字对象
 def __enter__(self):
  # 设置端口复用
  self.__sk.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True)
  # 绑定端口
  self.__sk.bind(self.__port)
  # 设置端口监听
  self.__sk.listen(128)
  # 返回套接字对象
  return self.__sk

 # 5.编写exit方法关闭套接字对象
 def __exit__(self, exc_type, exc_val, exc_tb):
  self.__sk.close()


def main():
 # 使用with关键字 并接受返回的套接字对象给sk
 with MySocket(8000) as sk:
  # 等待客户端连接
  clicent, ip_port = sk.accept()
  recv_data = clicent.recv(1024)
  print(recv_data.decode('utf-8'))
  # 编写HTTP响应报文
  http_line = 'HTTP/1.1 GET 200 OK\r\n'
  http_header = 'Server PWS/1.0\r\n'
  http_body = 'Welcome to index!\r\n'
  send_data = (http_line + http_header + '\r\n' + http_body).encode('utf-8')
  clicent.send(send_data)
  # 关闭客户端连接
  clicent.close()

# 编写程序入口
if __name__ == '__main__':
 main()