<python全栈开发基础>学习过程笔记【17d】生成器

>>> def f(x):
    return x**2

>>> [f(i) for i in range(10)]
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

>>> a=(1,2,3)
>>> x,y,z=a
>>> x
1
>>> y
2
>>> z
3

>>> b=[1,2,3]
>>> x1,y1,z1=b
>>> x1
1
>>> y1
2
>>> z1
3

>>> g=( i**2 for i in range(10))
>>> next(g)   
0
>>> next(g)
1
>>> next(g)
4
>>> next(g)
9
>>> next(g)
16
>>> next(g)
25
>>> next(g)
36
>>> next(g)
49
>>> next(g)
64
>>> next(g)
81
>>> next(g)    #越界
Traceback (most recent call last):
  File "<pyshell#34>", line 1, in <module>
    next(g)
StopIteration

>>> s=(i**2 for i in range(10))
>>> for i in s:   #内部：for in循环自动调用next，得到一个值，用i取这个值，使用之后，这个值被垃圾回收机制删除...所以很节省空间
    print(i)

    
0
1
4
9
16
25
36
49
64
81

>>> def a():
    print("ok1")
    yield 1   #yield返回一个值
    print("ok2")
    yield 2

    
>>> next(a())    #a()就是一个生成器，每一次next()都会运行到返回一个值为止
ok1
1
>>> next(a())
ok1
1

>>> for i in a():   #i每次存一个yield返回的值
    print(i)

    
ok1
1
ok2
2