def fib(max):
    n, a, b = 0, 0, 1
    while n < max:
        yield b
        a, b = b, a + b
        n = n + 1
    return 'done'


f = fib(10)
print(next(f))
print(next(f))
print(next(f))
print(next(f))

# 函数是顺序执行，遇到return语句或者最后一行函数语句就返回。而变成generator的函数，在每次调用next()的时候执行，遇到yield语句返回，再次执行时从上次返回的yield语句处继续执行。
def odd():
    print('step 1')
    yield 1
    print('step 2')
    yield(3)
    print('step 3')
    yield(5)

>>> o = odd()
>>> next(o)
step 1
1
>>> next(o)
step 2
3
>>> next(o)
step 3
5
>>> next(o)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

def test():
    print('开始啦')
    first = yield 1
    print('第一次', first)
    yield 2
    print('第二次')
    yield 3
    print('第三次')
# yield 1相当于return，控制的是函数的返回值
# yield可以接收send传过来的值

t = test()
res = t.__next__()
print(res)

t.send('hello')

# 三元表达式
name = 'alex'
res = 'SB' if name == 'alex' else '123'
print(res)

SB

# 列表解析
l1 = ['鸡蛋%s' % i for i in range(1, 10)]
l2 = ['鸡蛋%s' % i for i in range(1, 10) if i > 5]
# l3 = ['鸡蛋%s' % i for i in range(1, 10) if i > 5 else i] # 没有四元表达式
print(l1)
print(l2)

['鸡蛋1', '鸡蛋2', '鸡蛋3', '鸡蛋4', '鸡蛋5', '鸡蛋6', '鸡蛋7', '鸡蛋8', '鸡蛋9']
['鸡蛋6', '鸡蛋7', '鸡蛋8', '鸡蛋9']

# 生成器表达式
g = ('鸡蛋%s' % i for i in range(1, 10) if i > 5)
print(next(g))
print(next(g))
print(next(g))
print(next(g))

鸡蛋6
鸡蛋7
鸡蛋8
鸡蛋9

sum([x for x in range(1000000000)])  # 一次计算全部结果，占用大量内存
sum(x for x in range(1000000000))  # 一次计算一个结果，几乎不占内存