从Python3.x到Python2.7的“yield from”语义的后台端口
yieldfrom的Python项目详细描述
从python 3.x到python 2.7的yield from语义的后台端口
如果要在python 3.x中嵌套生成器，可以使用yield from
关键词。这允许您自动迭代子生成器和
透明地从顶级调用方传递异常和返回值
到最低的发电机。
def subgen():
yield 2
yield 3
def gen():
yield 1
yield from subgen() # Python 3.x only
yield 4
def main():
for i in gen():
print i,
>>> main()
... 1 2 3 4
此功能在Python2.x中不可用，我们使用
yieldfrom装饰器和助手From类：
from yieldfrom import yieldfrom, From
def subgen():
yield 2
yield 3
@yieldfrom
def gen():
yield 1
yield From(subgen())
yield 4
def main():
for i in gen():
print i,
>>> main()
... 1 2 3 4
高级用法允许使用
StopIteration。使用Return可以方便地做到这一点：
from yieldfrom import yieldfrom, From, Return
def subgen():
yield 2
yield 3
Return(100) # Raises `StopIteration(100)`
@yieldfrom
def gen():
yield 1
ret = (yield From(subgen()))
yield 4
yield ret
def main():
for i in gen():
print i,
>>> main()
... 1 2 3 4 100
子生成器可以嵌套在多个级别上，每个级别都需要额外的
装饰方式yieldfrom：
def subsubgen():
yield 2
@yieldfrom
def subgen():
yield From(subsubgen())
yield 3
@yieldfrom
def gen():
yield 1
yield From(subgen())
yield 4
def main():
for i in gen():
print i,
>>> main()
... 1 2 3 4
抛出到顶级生成器中的异常可以在 子生成器：
def subsubgen():
try:
yield 2
except ValueError:
yield 200
@yieldfrom
def subgen():
yield From(subsubgen())
yield 3
@yieldfrom
def gen():
yield 1
yield From(subgen())
yield 4
def main():
try:
g = gen()
while True:
i = g.next()
if i == 2:
i = g.throw(ValueError())
print i,
except StopIteration:
pass
>>> main()
... 1 200 3 4
注意，如果对简单的iterable（list）使用yield From()，
tuple等），则迭代器的各个成员将在
每次迭代（在这种情况下，您可能需要通常的yield）。
@yieldfrom
def gen():
yield From([1, 2, 3])
yield [1, 2, 3]
def main():
for i in gen():
print i
>>> main()
... 1
... 2
... 3
... [1, 2, 3]
将不可iterable对象传递给From将导致空
什么都不做的发电机。
@yieldfrom
def gen():
yield From(None)
yield 1
def main():
for i in gen():
print i
>>> main()
... 1
此模块是对以下python配方的改编：
http://code.activestate.com/recipes/576727
修改包括异常处理、命名、文档中的错误修复，
处理空发电机等
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