• Python学习笔记【第六篇】:迭代器、生成器、高阶函数、装饰器


     迭代器

      迭代器是访问集合元素的一种方式,迭代器从对象的第一个元素开始访问,知道所有元素被访问完成。迭代器只能往前访问,不能通过索引访问。

      类型内部使用__iter__()方法转为迭代器,使用__next__()取值。

    特点:

    1. 访问者不需要关心迭代器内部的结构,仅需通过next()方法不断去取下一个内容
    2. 不能随机访问集合中的某个值 ,只能从头到尾依次访问
    3. 访问到一半时不能往回退
    4. 便于循环比较大的数据集合,节省内存

    迭代器协议

      对象必须提供一个__next__方法执行该方法要么返回迭代中的下一项,要么返回一个Stopiteration异常以终止迭代

    迭代对象

      实现了迭代协议(for循环机制就基于可迭代协议)

    s_str = "hello world!"
    # 使用__iter__()方法转变为可迭代对象
    s_str_iter = s_str.__iter__()
    print(s_str_iter)
    # 使用可迭代对象里的next方法取值 (一直取到报异常:StopIteration)
    print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    # print(s_str_iter.__next__())
    
    # for 循环本质 1:先执行__iter__()转化为可迭代对象(遵循迭代协议) 2:然后依次执行__next__()方法 3:最后捕捉StopIteration异常
    
    dic = {"name": "张三", "age": 18, "sex": "男"}
    dic_iter = dic.__iter__()
    print(dic_iter.__next__())
    print(dic_iter.__next__())
    
    # 模拟for循环输出
    str = "1232456"
    str_iter = str.__iter__()
    
    while True:
        try:
            # print(str_iter.__next__())
            # 系统next()放和可迭代对象内部的__next__方法是一样的
            print(next(str_iter))
        except Exception as e:
            print(e)
            break
    

      

    生成器

      ·一个函数调用时返回一个迭代器,那么这个函数叫做生成器,如果函数中包含yield,那么这个函数就叫做生成器(自动生成或实现了可迭代协议),生成器的本质就是迭代器

      1:生成器函数:内部使用了yield关键字 2:生成器表达式:列表推导式,返回的就是生成器

    yield关键字

    def func():
        yield 1
        yield 2
        yield 3
        yield 4
    

      

    # 定义生成器
    def my_rang(start, stop, step=0):
        while start <= stop:
            yield start + step
            start += 1
    
    # 获取生成器
    number = my_rang(1, 7)
    # 依次获取值
    # print(number.__next__())
    # print(number.__next__())
    # print(number.__next__())
    # print(number.__next__())
    # print(number.__next__())
    # print(number.__next__())
    # print(number.__next__())
    # 便利获取值
    for i in my_rang(1, 7):
        print(i)
    

      

    print("========================生成100个包子案例===========================")
    
    
    def product_baozi():
        li = []
        for i in range(100):
            li.append("包子%s" % i)
        return li
    
    
    l = product_baozi()
    print(list(l))
    
    
    def product_pro():
        for i in range(100):
            print('正在生产包子.....')
            yield '以产包子%d' % i
            print('正在售卖包子')
    
    
    p_pro = product_pro()
    print(p_pro.__next__())
    print(p_pro.__next__())
    print(p_pro.__next__())
    
    # 生成器效率高 内存占用小
    #  yield总结:
    #   1、把函数做成迭代器
    #   2、对比return,可以返回多次值,可以挂起/保存函数的运行状态
    
    print("=========================人口普查案例=======================")
    
    
    # def get_population():
    #     res =[]
    #     with open("../files/population", "r", encoding="utf-8") as f:
    #         for i in f:
    #             res.append(i)
    #     return res
    #
    # p_gen = get_population()
    # print(p_gen)
    
    def get_population():
        with open("../files/population", "r", encoding="utf-8") as f:
            for i in f:
                yield i
    
    
    # 获取生成器
    p_gen = get_population()
    
    # 统计总人口数
    count = sum(eval(i)["population"] for i in p_gen)
    print(count)
    
    ppp = get_population()
    for i in ppp:
        print("%s 占统计人口的 %d %%" % (eval(i)['city'], count // eval(i)['population']))
    
    print('=========================跑步案例=======================')
    
    
    def run():
        i = 0
        while True:
            time.sleep(1)
            print('from run')
            yield i
            i += 1
    
    
    f = run()
    t = 0;
    while t <= 1:
        print(f.__next__())
        t += 1
    else:
        print("运行完成")
    
    # 几乎不占内存
    su = sum(i for i in range(100))
    print(su)
    
    # 三元表达式
    age = 10
    t = True if age > 10 else False
    
    # 列表推导式
    lit = [i for i in range(100) if i % 2 == 0]
    print(lit)
    
    
    def test():
        for i in range(4):
            yield i
    
    
    t = test()
    t1 = (i for i in t)
    t2 = (i for i in t1)
    print(list(t1))
    # t2为空,因为t2取自t1 ,在上面t1已经打印并且释放完了,所以t2为空
    print(list(t2))
    

    生产者和消费者 

    import time
    
    # 生产包子
    def consumer(name):
        print("我是【%s】,我准备开始吃包子了" % name)
        while True:
            baozi = yield
            time.sleep(1)
            print("%s 很开心把【%s】吃掉了" % (name, baozi))
    
    # 消费包子
    def producer():
        c1 = consumer("张三")
        c2 = consumer("李四")
        c2.__next__()
        c1.__next__()
        for i in range(10):
            time.sleep(1)
            c1.send('包子 %s' % i)
            c2.send('包子 %s' % i)
    
    
    producer()
    

      

    装饰器

      本质就是函数,为其它函数添加附加功能。2个原则,1:不修改被修饰的源代码,2:不修改被修饰函数的调用方式。

    装饰器 = 高阶函数 + 函数嵌套+ 闭包

    函数对象

         #1 可以被引用

      ·   #2 可以当作参数传递

         #3 返回值可以是函数

           #3 可以当作容器类型的元素

    函数嵌套

         在函数内部再次定义函数     

    def text1():
        def text2():
            print('我是在text1函数内部定义的text2函数。')
        text2()
    text1()
    

      

    高阶函数

      函数接收的参数是一个函数名称或者函数的返回值是一个函数名

    def text1():
        def text2():
            print('我是在text1函数内部定义的text2函数。')
    
        return text2  # 返回text2函数内存地址
    
    
    # 调用
    
    # text1()()
    # text1() 是调用text返回的都是text2的地址,
    t = text1()
    print(t)
    # 真正调用函数
    t()
    

      

     闭包

      在第五篇函数中有讲到.......

    装饰器代码案例

       为一个函数添加一个运行时间计算的方法

    def text(func):
        def text1():
            start_time = time.time()
            func()
            end_time = time.time()
            print("foo函数运行时间为:%s" % (end_time - start_time))
    
        return text1
     
    def foo():
        print('来自foo函数运行模块....')
    
     
    foo = text(foo)
    foo()
     
    

      

    @装饰器名称  ----------》python语法糖

    def text(func):
        def text1():
            start_time = time.time()
            func()
            end_time = time.time()
            print("foo函数运行时间为:%s" % (end_time - start_time))
    
        return text1
    
    
    @text  # foo = text(foo)
    def foo():
        print('来自foo函数运行模块....')
    
    
    # @text 相当于foo = text(foo)
    # foo = text(foo)
    # foo()
    # 为改变调用方式
    foo()
    

      

     装饰器带参数、返回值

    from 数据库操作.MySqlHelper import MySqlHelper
    from 数据库操作.RedisHelper import RedisHelper
    from hashlib import sha1
    
    
    ## 装饰器返回值
    # def text1(func):
    #     def text2():
    #         func()
    #         return "text2返回值"
    #     return text2
    #
    # @text1
    # def text():
    #     print('这是text1')
    #
    # t = text()
    # print(t)
    
    # # 装饰器带参数
    # def text1(func):
    #     def text2(a,b):
    #         func(a,b)
    #         return "text2返回值"
    #     return text2
    #
    # @text1
    # def text(a,b):
    #     print('这是text1')
    #     print("a+b=%s"%(a+b))
    #
    # t = text(13,14)
    # print(t)
    
    
    # 装饰器带参数
    def text1(func):
        def text2(*args, **kwargs):
            func(*args, **kwargs)
            return "text2返回值"
    
        return text2
    
    
    @text1
    def text(a, b):
        print('这是text1')
        print("a+b=%s" % (a + b))
    
    
    text(15, 18)
    # t = text(13, 14)
    # print(t)
    

      

    装饰器综合案例

     不同数据库的登录验证

    # -*- coding: utf-8 -*-
    
    # 声明字符编码
    # coding:utf-8
    from 数据库操作.MySqlHelper import MySqlHelper
    from 数据库操作.RedisHelper import RedisHelper
    from hashlib import sha1
    
    print("========================验证功能========================")
    
    # 定义登录返回的消息格式
    result_msg = {"success": False, 'message': ''}
    
    
    # 定义文件读取生成器
    def file_yeid():
        with open("../files/users", 'r', encoding='utf-8') as f:
            for row in f:
                yield row
    
    
    # file登录验证
    def file_login(user_name, user_pwd):
        # 获取文件生成器
        users = file_yeid()
        for row in users:
            try:
                user = eval(row)
                print(user)
                if user['user_name'] == user_name:
                    if user['user_pwd'] == user_pwd:
                        result_msg['success'] = True
                        result_msg['message'] = '登录成功'
                    else:
                        result_msg['success'] = False
                        result_msg['message'] = '密码错误'
                    break
            except Exception as e:
                print('账号文件内容异常。。。。')
        else:
            result_msg['success'] = False
            result_msg['message'] = '用户名不存在'
        return result_msg
    
    
    # redis登录验证
    def redis_login(user_name, user_pwd):
        redis = RedisHelper(host="118.24.53.196", port=6379)
        name_value = redis.get(user_name)
        print("redis用户名:%s"%name_value)
        if name_value is None:
            result_msg['success'] = False
            result_msg['message'] = '用户名不存在'
        else:
            name_value = name_value.decode("utf8")
            if name_value == user_pwd:
                result_msg['success'] = True
                result_msg['message'] = '登录成功'
            else:
                result_msg['success'] = False
                result_msg['message'] = '密码错误'
        return result_msg
    
    
    # MySql登录验证
    def mysql_login(user_name, user_pwd):
        # 从数据库查询
        sql_helper = MySqlHelper(host='127.0.0.1', user='admin', password='123456', db='python')
        sql = "SELECT * FROM users WHERE uname = %s"
        params = [user_name]
        user_info = sql_helper.fetchall(sql, params)
        print(user_info)
        if user_info is None:
            result_msg['success'] = False
            result_msg['message'] = '用户名不存在'
        elif user_info[0][2] == user_pwd:
            result_msg['success'] = True
            result_msg['message'] = '登录成功'
    
        else:
            result_msg['success'] = False
            result_msg['message'] = '密码错误'
    
        return result_msg
    
    
    def login_verification(db_type):
        def login_gener(func):
            # 接收用户输入
            user_name = input("请输入用户名:")
            user_pwd = input("请输入密码:")
            # 用户密码加密操作
            s1 = sha1()
            s1.update(user_pwd.encode('utf-8'))
            pwd_sha = s1.hexdigest()
            print("密码加密后:%s" % pwd_sha)
    
            def login(*args, **kwargs):
    
                resut = ""
                if db_type == 'file_db':
                    resut = file_login(user_name, pwd_sha)
                    print('file登录信息:%s' % resut)
                elif db_type == 'redis_db':
                    resut = redis_login(user_name, pwd_sha)
                    print('redis登录信息:%s' % resut)
                elif db_type == 'mysql_db':
    
                    resut = mysql_login(user_name, pwd_sha)
                    print('mysql登录信息:%s' % resut)
                else:
                    print('暂无当前数据库类型的验证!!')
                    return
                if resut['success'] == True:
                    func(user_name)
                else:
                    func("游客")
    
            return login
    
        return login_gener
    
    
    @login_verification(db_type='redis_db')
    def index(name):
        print("欢迎[%s]来到首页。。。。。。。。。" % name)
    
    @login_verification(db_type='redis_db')
    def home(name):
        print("欢迎[%s]来到家目录" % name)
    
    
    # index("hehe")
    home()
    
    # 单个测试
    # print(file_login('lisi', 'c3be7cf2877085fed38e0ec93b009e547e2929e0'))
    # print(redis_login('admin1', 'c3be7cf2877085fed38e0ec93b009e547e2929e'))
    # print(mysql_login('admin','c3be7cf2877085fed38e0ec93b009e547e2929e0'))# 密码为:123
    

    MySqlHelper: 

    # -*- coding: utf-8 -*-
    
    # 声明字符编码
    # coding:utf-8
    import pymysql
    
    class MySqlHelper(object):
    
        def __init__(self, host, user, password, db, charset='utf8', port=3306):
            """ 初始化 """
            self.host = host ,  # 服务器名称
            self.port = port # 3306, 3306
            self.user = user ,  # 用户名
            self.password = password ,  # 密码
            self.db = db #'python',  # 数据库名称
            self.charset = charset #'utf8'  # 字符编码
            self.conn = None
            self.cursor = None
    
        def connect(self):
            """链接数据库"""
            db_config = {
                'host': self.host,  # 服务器名称
                'port': self.port,  # 3306
                'user': self.user,  # 用户名
                'password': self.password,  # 密码
                'db': self.db,  # 数据库名称
                'charset': self.charset  # 字符编码
            }
            self.conn = pymysql.connect(**db_config)
            self.cursor = self.conn.cursor()
    
        def close(self):
            """关闭数据库"""
            self.cursor.close()
            self.conn.close()
    
        def execute(self, sql, params=[]):
            """执行数据库 增删改"""
            try:
                self.connect()
                self.cursor.execute(sql, params)
                self.conn.commit()
                self.close()
                print("OK")
            except Exception as e:
                print("异常信息如下:")
                print("%s" % e)
    
        def fetchall(self, sql, params=[]):
            """数据查询"""
            try:
                self.connect()
                self.cursor.execute(sql, params)
                result = self.cursor.fetchall()
                self.close()
                return result
            except Exception as e:
                print('%s' % e)
    

     

    RedisHelper

    # -*- coding: utf-8 -*-
    
    # 声明字符编码
    # coding:utf-8
    
    from redis import *
    # 这种连接不需要指定数据库及密码
    # = StrictRedis(host="127.0.0.1", port=6379)
    
    class RedisHelper():
        def __init__(self, host, port):
            self.host = host
            self.port = port
            self.__redis = StrictRedis(host, port)
    
        def set(self, key, value):
            self.__redis.set(key, value)
    
        def get(self, key):
            return self.__redis.get(key)
    

      

     

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  • 原文地址:https://www.cnblogs.com/wendj/p/9232467.html
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