yield | 易学教程

python高级特性

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文章目录生成式生成式小案例生成器生成器小案例生产者-消费者模型生成器、迭代器与可迭代对象闭包装饰器生成式列表生成式：用来生成列表的特定语法形式的表达式。是Python提供的一种生成列表的简洁形式, 可快速生成一个新的list 普通的语法格式： [exp for iter_var in iterable] #列表生成式：生成100个1～50之间的随机数值。 #先使用空列表循环100次每循环一次在random.randint(1,50)中选一个值保存到[]中 print([random.randint(1,50) for i in range(1,100)]) 执行结果： [42, 8, 22, 16, 34, 8, 37, 39, 31, 30, 7, 3, 11, 17, 39, 4, 8, 8, 16, 5, 12, 27, 15, 35, 1, 9, 5, 17, 41, 9, 14, 22, 29, 16, 30, 30, 44, 40, 32, 30, 20, 2, 28, 35, 19, 21, 38, 35, 12, 42, 30, 35, 9, 35, 34, 25, 44, 6, 8, 26, 26, 13, 19, 15, 37, 40, 15, 44, 1, 16, 27, 38, 15, 44, 5, 39, 23, 25, 7,

python中 yield 的用法（简单、清晰）

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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 ******************** 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

Using multiple yields to insert content

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问题 I am trying to insert content on my page with yield but every time action removes whole content from the page. I have one main yield which is working fine: <body> <%= render 'layouts/header' %> <div class="container"> <%= yield %> <%= render 'layouts/footer' %> </div> </body> But inside that new content which is displayed on one page I have another yield : <div class="container"> <%= render 'admins/menu' %> <%= yield :admin %> </div> When user clicks on the menu which is rendered, new content

How do yield works in Python C code, good & bad part

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问题 Recently I've been looking into the code of Python. I know how to use generators (next, send and etc..), but it's fun to understand it by reading the Python C code. I found the code in Object/genobject.c, and it's not that hard (but still not easy) to understand. So I want to know how it really works, and make sure I do not have a misunderstanding about generators in Python. I know everything calls static PyObject * gen_send_ex(PyGenObject *gen, PyObject *arg, int exc) and the result is

Python中的yield

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引用（http://www.jianshu.com/p/d09778f4e055）阅读别人的python源码时碰到了这个yield这个关键字，各种搜索终于搞懂了，在此做一下总结：通常的for...in...循环中，in后面是一个数组，这个数组就是一个可迭代对象，类似的还有链表，字符串，文件。它可以是mylist = [1, 2, 3]，也可以是mylist = [x*x for x in range(3)]。它的缺陷是所有数据都在内存中，如果有海量数据的话将会非常耗内存。生成器是可以迭代的，但只可以读取它一次。因为用的时候才生成。比如 mygenerator = (x*x for x in range(3))，注意这里用到了()，它就不是数组，而上面的例子是[]。我理解的生成器(generator)能够迭代的关键是它有一个next()方法，工作原理就是通过重复调用next()方法，直到捕获一个异常。可以用上面的mygenerator测试。带有 yield 的函数不再是一个普通函数，而是一个生成器generator，可用于迭代，工作原理同上。 yield 是一个类似 return 的关键字，迭代一次遇到yield时就返回yield后面(右边)的值。重点是：下一次迭代时，从上一次迭代遇到的yield后面的代码(下一行)开始执行。简要理解：yield就是 return

Can yield produce multiple consecutive generators?

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问题 Here are two functions that split iterable items to sub-lists. I believe that this type of task is programmed many times. I use them to parse log files that consist of repr lines like ('result', 'case', 123, 4.56) and ('dump', ..) and so on. I would like to change these so that they will yield iterators rather than lists. Because the list may grow pretty large, but I may be able to decide to take it or skip it based on first few items. Also, if the iter version is available I would like to

Can yield produce multiple consecutive generators?

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Python: Yield in multiprocessing Pool

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问题 I've to Parallelize a function which involves a certain "yield". This is only a simple replica of the whole program that I've to work on, but sums up the problems i'm facing. Here I'm try to understand multiprocessing, apply_async and yield for my project In this example I've used a multiprocessing.pool and have used the apply_async to parallelize. I've put some print statements in the "parallel" function, but they aren't getting printed. When i replace yield with return the the print

What is the difference between “yield return 0” and “yield return null” in Coroutine?

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问题 I'm new and a bit confused about " yield ". But finally I understand how it worked using WaitForSeconds but I can't see the difference between of " yield return 0 " and " yield return null ". are both them waiting for the next frame to execute? sorry for my bad English. Thank you very much. 回答1: Both yield return 0 and yield return null yields for a single frame. The biggest difference is that yield return 0 allocates memory because of boxing and unboxing of the 0 that happens under the hood,

C# 迭代器中yield关键字的使用

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上一篇笔记：C# 迭代器 https://blog.csdn.net/dayuhaitang1/article/details/103593599 在上一篇笔记中，演示的是C#1.0中的迭代器的创建方法，而在C#2.0中经过了改进之后又有了新的书写形式，所以写一篇笔记记录一下。一、yield关键字 C#2.0中的迭代器的实现代码相较于C#1.0有了很大幅度的减少，之所以会这样这主要就是引入了yield关键字。yield关键字其实质就是在编译器对代码进行编译时，遇到yield关键字时就是在提示编译器这是实现一个迭代器块的方法。也就是将本来应该由我们创建嵌套类实现IEnumerator的工作，让编译器帮我们做了而已。但是这样的确使我们为实现迭代器减少了很大的工作量，使我们能更好的运用迭代器这一工具。二、利用yield实现迭代器 class Program { static void Main ( string [ ] args ) { object [ ] values = { "a" , "b" , "c" , "d" , "e" } ; IterationSample collection = new IterationSample ( values , 3 ) ; foreach ( var item in collection ) { Console . WriteLine

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