Python 产生多个值
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Yield multiple values
提问by Shyam Sunder
Can't we yield more than one value in the python generator functions?
我们不能在 python 生成器函数中产生多个值吗？
Example,
例子，
In [677]: def gen():
.....: for i in range(5):
.....: yield i, i+1
.....:
In [680]: k1, k2 = gen()
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-680-b21f6543a7e9> in <module>()
----> 1 k1, k2 = a()
ValueError: too many values to unpack
This works as follows:
其工作原理如下：
In [678]: b = a()
In [679]: list(b)
Out[679]: [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5)]
Same results even when I do this:
即使我这样做，结果也一样：
In [692]: def a():
for i in range(5):
yield i
yield i+1
Thanks.
谢谢。
采纳答案by Jon Clements
Because gen()returns a generator (a single item - so it can't be unpacked as two), it needs to be advanced firstto get the values...
因为gen()返回一个生成器（单个项目 - 所以它不能被解包为两个），它需要先提前获取值......
g = gen()
a, b = next(g)
It works with listbecause that implicitly consumes the generator.
它可以工作，list因为它隐式消耗了生成器。
Can we further make this a generator? Something like this:
我们可以进一步使它成为生成器吗？像这样的东西：
g = gen();
def yield_g():
yield g.next();
k1,k2 = yield_g();
and therefore list(k1)would give [0,1,2,3,4]and list(k2)would give [1,2,3,4,5].
因此list(k1)会给予[0,1,2,3,4]并且list(k2)会给予[1,2,3,4,5]。
Keep your existing generator, and use izip(or zip):
保留您现有的生成器，并使用izip（或压缩）：
from itertools import izip
k1, k2 = izip(*gen())
回答by David Zwicker
Your function genreturns a generator and not values as you might expect judging from the example you gave. If you iterate over the generator the pairs of values will be yielded:
您的函数gen返回一个生成器而不是值，正如您从您提供的示例中所期望的那样。如果您迭代生成器，将产生成对的值：
In [2]: def gen():
...: for i in range(5):
...: yield i, i+1
...:
In [3]: for k1, k2 in gen():
...: print k1, k2
...:
0 1
1 2
2 3
3 4
4 5
回答by forzagreen
Use yield from
用 yield from
def gen():
for i in range(5):
yield from (i, i+1)
[v for v in gen()]
# [0, 1, 1, 2, 2, 3, 3, 4, 4, 5]
The python docssay:
在python文档说：
When
yield from <expr>is used, it treats the supplied expression as a subiterator.
当
yield from <expr>被使用时，它把所提供的表达式作为subiterator。
