迭代器,三元表达式,列表生成式,字典生成式,生成器,递归(没深入理解)

#for 循环的原理
s = 'hello'
iter_s = s.__iter__()

while True:
    try:
        print(iter_s.__next__())
    except StopIteration:
        break                     #如果报错停止

for a in range(1,19):
    if a == 10:
        print('等于10')
    else:
        print('不等于10')
 #三元表达式
for a in range(1,19):
    print('等于10') if a ==10 else print('不等于10')

lis = [i for i in range(1,10)]
print(lis)
#[1, 2, 3, 4, 5, 6, 7, 8, 9]

dic = dict.fromkeys([1,2,1],1) #他会强制吧前面的变成集合
print(dic)
#{1: 1, 2: 1}

dic = {i:i for i in range(1,10)} #for 前面为每次生成的内容
print(dic)
#{1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}

keys = ['name', 'age', 'gender']
values = ['nick', 19, 'male']
a = zip(keys,values)
print(a)   #<zip object at 0x000000000265DB48> 只是个地址可以减少内存
dic = {x:y for x,y in a}
print(dic)  #{'name': 'nick', 'age': 19, 'gender': 'male'}

#我们可以这样写
keys = ['name', 'age', 'gender',1]
values = ['nick',i9, 'male']
dic ={x:y for x,y in zip(keys,values)}
print(dic)
 #{'name': 'nick', 'age': 19, 'gender': 'male'}
#从这里我们可以知道zip他会根据两个或多个存多个值按照FOR循环,从左往右一一对应组成键值对,按最小长度的值来决定键值对的个数

#用yield来写出range函数
def range(end,start=0,step=1):
    if start !=0:
        end,start =start,end
        if step >0:
            count = start
            while count < end:
                yield count
                count += step
        elif step <0:
            count = end
            while count >= start:
                yield count
                count += step               
        else:
            raise('不能为0')
        return
    count = start
    while count < end:
        yield count
        count += step

generator = (i for i in range(10))
print(generator.__next__())
# 0

def func_1():
    print('1')
    func_1()
func_1()  #会进入死循环

def foo(n):
    print('from foo',n)
    foo(n+1)
foo(0)

def bar():
    print('from bar')
    foo()
    
def foo():
    print('from foo')
    bar()
    
bar()