python基础

Posted 2021-02-07 萌萌~哒

一、私有

class DB:
    port = 3306  #类变量
    def __init__(self):
        self.host = ‘127.0.0.1‘
        self.__user = ‘root‘  #实例变量，成员变量
        self.__password = ‘123456‘
        self.db = ‘xx‘
        # self.__help()
    def sql(self,sql):
        self.__help()
        print(‘执行sql‘)
    def __help(self):
        print(self.host)
        print(self.__user)
        print(self.__password)
        print(self.db)
        print(self.port)

    def get_port(self):  #实例方法
        print(self.port)

    @classmethod
    def help(cls):
        print(‘这个类是用来连接数据库的，它的用法是xxx‘)
        print(‘cls的内存地址‘,id(cls))

DB.help()

二、多线程及多线程下载网页

import threading
import time
def run():
    time.sleep(5)
    print(‘over‘)

start_time = time.time()
for i in range(100):
    t = threading.Thread(target=run)
    t.start()

print(‘运行的时候几个线程‘,threading.activeCount() ) # 1
#threading.activeCount就是当前有几个线程
while 1:
    if threading.active_count()==1:
        break


print(‘这时候几个线程‘,threading.activeCount()) # 2
end_time = time.time()
print(‘run time =‘,end_time - start_time) #

print(‘运行结束‘)


‘‘‘ 第一种for循环主线程等待子线程运行结束
start_time = time.time()
ths = [] #100
for i in range(100):
    t = threading.Thread(target=run) #实例化一个线程，
    t.start()#启动这个线程
    ths.append(t)

for t in ths:
     t.join() #循环等待每个子线程执行结束
end_time = time.time()
print(‘run time =‘,end_time - start_time)
‘‘‘

    # start_time = time.time()
# run()
# run()
# run()
# run()
# end_time = time.time()
# print(‘run time =‘,end_time - start_time)

import requests
import time
import threading
def download_html(url,file_name):
    res = requests.get(url)
    with open(file_name+‘.html‘,‘wb‘) as fw:
        fw.write(res.content)
    print(‘【%s】下载完成‘%file_name)

urls={
    ‘nnzhp‘:‘http://www.nnzhp.cn‘,
    ‘cc‘:‘http://www.cc-na.cn‘,
    ‘dsx‘:‘http://www.imdsx.cn‘,
    ‘besttest‘:‘http://www.besttest.cn‘,
}

start_time = time.time()

for file_name,url in urls.items():
    t = threading.Thread(target=download_html,args=(url,file_name))
    #args=(url,) #单个参数的时候，一定要这么写
    t.start()
while threading.active_count()!=1:
    pass

end_time = time.time()
print(‘run time =‘,end_time - start_time)

    #单线程
# start_time = time.time()
# for k,v in urls.items():
#     download_html(url=v,file_name=k)
# end_time = time.time()
# print(‘run time =‘,end_time - start_time)