迭代器

count = 0while True:    if count ==101:        break    print(count)    count += 1    

python中一切皆对象

height = 180salary = 3.2name = ‘nick‘hobby_list1 = [‘run‘,‘read‘]hobby_tup = (‘run‘,‘read‘)info_dict1 = {‘name‘:‘nick‘,‘weight‘:140}hobby_set = {‘read‘,‘run‘,‘run‘}?def func():    pass?# w和a模式都会自动生成文件f = open(‘test.txt‘,‘w‘,encoding=‘utf8‘)

可迭代对象：只要拥有iter方法的对象就是可迭代对象

height.__iter__salary.__iter__func.__iter__name.__iter__()hobby_list.__iter__()hobby_set.__iter__()hobby_tup.__iter__()info_dict.__iter__()f.__iter__()

字符串、列表、元祖、字典、集合、文件都是可迭代对象

hobby_list = [‘run‘,‘read‘]hobby_list_iter = hobby_list.__iter__()  # 把列表变成可迭代对象# print(hobby_list_iter.__next__())# print(hobby_list_iter.__next__())# print(hobby_list_iter.__next__())?# for k in info_dict:#     print(k)info_dict = {‘name‘:‘nick‘,‘weight‘:140}info_dict_iter = info_dict.__iter__()# print(info_dict_iter.__next__())# print(info_dict_iter.__next__())# print(info_dict_iter.__next__())

next其实是在遍历和迭代对象的元素，一旦遍历完报错

迭代器对象：拥有 iter _ 方法，可迭代对象拥有next_方法的才是迭代器对象，文件本身就是迭代器对象

hobby_list2 = [‘run‘,‘read‘]# count = 0# while True:#     print(hobby_list2[count])##     count += 1##     if count == len(hobby_list2):#         break?# for循环不依赖索引取值?# 这一段代码如果用c写,就是for循环的原理hobby_list2 = [‘run‘,‘read‘]hobby_list2_iter = hobby_list2.__iter__()while True:    try:        print(hobby_list2_iter.__next__())    except:        break?for i in hobby_list2:  # hobby_list2,把hobby_list2转化为可迭代对象    print(i)???print(hobby_list2) # 一筐鸡蛋print(hobby_list2.__iter__()) # 相比较列表,它节省内存空间,老母鸡?print(hobby_list2_iter)print(hobby_list2_iter.__iter__().__iter__().__iter__())  # 迭代器对象使用iter方法后是迭代器对象本身

可迭代对象：拥有iter方法的对象就是可迭代对象，推到：可迭代对象不一定是迭代器对象

迭代器对象：拥有iter方法的和next方法的就是迭代器对象，推导：迭代器对象一定是可迭代对象

文件即可迭代对象，又是迭代器对象

三元表达式（三目表达式）

dog_name = ‘xiaogou‘?if dog_name ==‘fenggou‘:    print(‘远离他‘)else:    print(‘盘他‘)    #不推荐使用print(‘远离他‘) if dog_name ==‘fenggou‘ else print(‘盘他‘)?# 列表推导式# lis = []## for i in range(100):#     lis.append(i)## print(lis)?# lis = [i*2 for i in range(100)]# print(lis)# 千万不要写这样的东西,否则真的会被骂傻逼lis1 = [i * 2 if i > 50 else i for i in range(100)]print(lis1)

字典生产式

?lis = [i for i in range(10)]print(lis)?dic2= dict.fromkeys([1,2,3,4],2)print(dic2)dic = {i:i**2 for i in range(10)}for i in dic.items():    print(i)?拉链函数res = zip(‘abcd‘,[1,2,3,4])dic = dict()for k,v in res:    dic[k] = v?print(dic)?print({k:v for k,v in zip(‘abcd‘,[1,2,3,4])})??

递归

def f2():    print(‘from f2‘)    # 递归： 函数掉函数自己，类似于循环，但是这个循环必须有结束条件import timedef f1(x): # x=0    print(x) # 0 1    # time.sleep(1)    x += 1 # 1 2    if x ==101:        return    f1(x) # x=1        def f2():    f1()f1(0)?def guess_age(age,count):    age -= 2    count -= 1    if count ==1:        print(age)        return    guess_age(age,count)        guess_age(38,5)def guess_age(count): #age ==38 count =5    #age -=2 #36.34.32.30    count -= 1    if count ==1:        # print(age)        return 26    return guess_age(count) +2??res = guess_age(5)print(res)

def guess_age(count):# 5    count -= 1# 4    if count ==1:        return 26    return guess_age(count) +2#  guess_age(4) + 2 # guess_age(3) + 2 # guess_age(2) + 2# guess_age(5) = guess_age(4) + 2  = (guess_age(3) + 2) + 2 = ((guess_age(2) + 2) + 2) + 2 = 26 + 2 + 2 + 2 = 32# 26 + 2 =guess_age(3)=28  # 28+2=guess_age(4) = 30 # 30 + 2res = guess_age(5)print(res)

原文地址：https://www.cnblogs.com/zrx19960128/p/10970137.html