yield

In my everlasting quest to suck less I'm trying to understand the "yield" statement, but I keep encountering the same error. The body of [someMethod] cannot be an iterator block because 'System.Collections.Generic.List< AClass>' is not an iterator interface type. This is the code where I got stuck: foreach (XElement header in headersXml.Root.Elements()){ yield return (ParseHeader(header)); } What am I doing wrong? Can't I use yield in an iterator? Then what's the point? In this example it said that List<ProductMixHeader> is not an iterator interface type. ProductMixHeader is a custom class,

1.send方法 1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 # 启动生成器有两种方法，next()和send() 4 5 6 def gen_func(): 7 # 1.可以产出值 2.可以接收值(调用方传递的值) 8 html = yield 'http://projectsedu.com' 9 print(html) 10 yield 2 11 yield 3 12 return 'zy' 13 14 15 if __name__ == '__main__': 16 # 生成生成器对象 17 gen = gen_func() 18 # 在调用send发送非None值之前，我们必须启动一次生成器，方式有两种1.gen.send(None)，2.next(gen) 19 url = gen.send(None) 20 # download html 21 html = 'zy' 22 # send()可以传递值进入生成器内部，同时重启生成器执行到下一个yield位置 23 print(gen.send(html)) 24 25 # print(next(gen)) 26 # print(next(gen)) 27 # print(next(gen)) zy 2 2.close方法 1 #!/usr/bin/env

How might one implement C# yield return using Scala continuations? I'd like to be able to write Scala Iterator s in the same style. A stab is in the comments on this Scala news post , but it doesn't work (tried using the Scala 2.8.0 beta). Answers in a related question suggest this is possible, but although I've been playing with delimited continuations for a while, I can't seem to exactly wrap my head around how to do this. Before we introduce continuations we need to build some infrastructure. Below is a trampoline that operates on Iteration objects. An iteration is a computation that can

转： https://blog.csdn.net/mieleizhi0522/article/details/82142856 首先我要吐槽一下，看程序的过程中遇见了yield这个关键字，然后百度的时候，发现没有一个能简单的让我懂的，讲起来真TM的都是头头是道，什么参数，什么传递的，还口口声声说自己的教程是最简单的，最浅显易懂的，我就想问没有有考虑过读者的感受。 接下来是正题： 首先，如果你还没有对yield有个初步分认识，那么你先把yield看做“return”，这个是直观的，它首先是个return，普通的return是什么意思，就是在程序中返回某个值，返回之后程序就不再往下运行了。看做return之后再把它看做一个是生成器（generator）的一部分（带yield的函数才是真正的迭代器），好了，如果你对这些不明白的话，那先把yield看做return,然后直接看下面的程序，你就会明白yield的全部意思了： def foo(): print("starting...") while True: res = yield 4 print("res:",res) g = foo() print(next(g)) print("*"*20) print(next(g)) 就这么简单的几行代码就让你明白什么是yield，代码的输出这个： starting... 4 **********

This question already has an answer here: Is there ever a reason to not use 'yield return' when returning an IEnumerable? There are several useful questions here on SO about the benefits of yield return . For example, Can someone demystify the yield keyword Interesting use of the c# yield keyword What is the yield keyword I'm looking for thoughts on when NOT to use yield return . For example, if I expect to need to return all items in a collection, it doesn't seem like yield would be useful, right? What are the cases where use of yield will be limiting, unnecessary, get me into trouble, or

I've got a tree-like structure. Each element in this structure should be able to return a Enumerable of all elements it is root to. Let's call this method IEnumerable<Foo> GetAll() . So if we have A <-- topmost root / \ B C / \ / \ D E F G a call to GetAll on element C returns {C, F, G} (fixed order of elements would be nice, but is not needed). I guess everybody knew that already. The current implementation of GetAll looks like this: public IEnumerable<Foo> GetAll () { yield return this; foreach (Foo foo in MyChildren) { foreach (Foo f in foo.GetAll ()) { yield return f; } } } In an earlier

python~函数详解2 1 生成器函数 定义 如果函数有yield这个关键字,就是生成器函数.生成器函数() 获取的是生成器,不执行函数 须知 yield和return一样,都可以返回数据,但是不会彻底中断函数,分段进行函数处理 继续执行 函数(迭代器) __next__() __send__(参数)//和next具有同一个功能,还添加了给上一个值赋值功能 def func() print(a) a=yield 1 //yield特殊定义 print (b) b=yield 2说 gen=funct//不会执行函数 a=gen.__next___()//继续执行函数 a=gen.__send__("wdadaw") 注意 1 书写生成器函数最后必须以yield结尾,否则会报异常 2 最后一个yield不能传值,yield会打印输出 3 可以通过for,list循环访问对象,则证明for和list循环自带__next__ 2 推导式 一句话生成列表 list=["python"+star(i) for i in range(10)] 1 构成方式 结果 for循环 判断 2 多重for循环并排写即可 一句话生成字典 dick={a[key]:value for i in range(len(list)) } 语法构成 {key:value 循环 条件判断} 3 生成器表达式 1

原文链接：https://blog.csdn.net/mieleizhi0522/article/details/82142856 首先，如果你还没有对yield有个初步分认识，那么你先把yield看做“return”，这个是直观的，它首先是个return，普通的return是什么意思，就是在程序中返回某个值，返回之后程序就不再往下运行了。看做return之后再把它看做一个是生成器（generator）的一部分（带yield的函数才是真正的迭代器），好了，如果你对这些不明白的话，那先把yield看做return,然后直接看下面的程序，你就会明白yield的全部意思了： def foo(): print("starting...") while True: res = yield 4 print("res:",res) g = foo() print(next(g)) print("*"*20) print(next(g)) 就这么简单的几行代码就让你明白什么是yield，代码的输出这个： starting... 4 ******************** res: None 4 我直接解释代码运行顺序，相当于代码单步调试： 1.程序开始执行以后，因为foo函数中有yield关键字，所以foo函数并不会真的执行，而是先得到一个生成器g(相当于一个对象) 2.直到调用next方法