标签：推荐   test   while   encoding   odi   可迭代对象   三元   name   span   

迭代器

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

python中一切皆对象

height = 180
salary = 3.2
name = ‘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 time
def 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 + 2
res = guess_age(5)
print(res)

6.3 迭代 递归

标签：推荐   test   while   encoding   odi   可迭代对象   三元   name   span   

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