Question

我知道yield会将函数转换为生成器，但yield表达式本身的返回值是多少？例如：

def whizbang(): 
    for i in range(10): 
        x = yield i

此函数执行时变量x的值是多少？

我已经阅读了Python文档：http://docs.python.org/reference/simple_stmts.html#grammar-token-yield_stmt并且似乎没有提到yield表达式本身的价值。

Answer 1

您还可以send生成器的值。如果未发送任何值，则x为None，否则x将采用已发送的值。以下是一些信息：http://docs.python.org/whatsnew/2.5.html#pep-342-new-generator-features

>>> def whizbang():
        for i in range(10):
            x = yield i
            print 'got sent:', x


>>> i = whizbang()
>>> next(i)
0
>>> next(i)
got sent: None
1
>>> i.send("hi")
got sent: hi
2

Answer 2

此代码将产生一些输出

def test():
    for i in range(10):
        x = yield i

t = test()
for i in test():
    print i

Answer 3

这是一个从一个大的cahce

给出缓冲输出的yield的例子

#Yeild

def a_big_cache():
    mystr= []
    for i in xrange(100):
        mystr.append("{}".format(i))
    return mystr

my_fat_cache = a_big_cache()

def get_in_chunks(next_chunk_size):
    output =[]
    counter = 0
    for element in my_fat_cache:
        counter += 1
        output.append(element)
        if counter == next_chunk_size:
            counter = next_chunk_size
            next_chunk_size+= next_chunk_size
            yield output
            del output[:]

r = get_in_chunks(10)
print next(r)
print next(r)

输出

[＆＃39; 0＆＃39;，＆＃39; 1＆＃39;，＆＃39; 2＆＃39;，＆＃39; 3＆＃39;，＆＃39; 4＆＃39;，＆＃39; 5＆＃39;，＆＃39; 6＆＃39;，＆＃39; 7＆＃39;，＆＃39; 8＆＃39;，＆＃39; 9＆＃39;]

[＆＃39; 10＆＃39;，＆＃39; 11＆＃39;，＆＃39; 12＆＃39;，＆gt; ＆＃39; 13＆＃39;，＆＃39; 14＆＃39;，＆＃39; 15＆＃39;，＆＃39; 16＆＃39;，＆＃39; 17＆＃39;，＆＃39; 18＆＃39;，＆＃39; 19＆＃39;]

Python中yield表达式的结果是什么？

3 个答案: