【Python】Python中的注解“@”

<p style="border:0px;line-height:1.7;color:rgb(51,51,51);font-family:'-apple-system','SF UI Text',Arial,'PingFang SC','Hiragino Sans GB','Microsoft YaHei','WenQuanYi Micro Hei',sans-serif;font-size:16px;">python3.0之后加入新特性Decorators，以@为标记修饰function和class。有点类似c++的宏和java的注解。Decorators用以修饰约束function和class，分为带参数和不带参数，影响原有输出，例如类静态函数我们要表达的时候需要函数前面加上修饰@staticmethod或@classmethod,为什么这样做呢？下面用简单的例子来看一下，具体内容可以查看：<a href="http://www.python.org/dev/peps/pep-0318/" rel="nofollow" style="background-color:transparent;color:rgb(15,153,50);border:0px;">官方解释

<h3 style="font-family:'-apple-system',sans-serif;line-height:1.7;color:rgb(47,47,47);font-size:18px;border:0px;">不带参数的单一使用<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,'Bitstream Vera Sans Mono','DejaVu Sans Mono',Monaco,Consolas,monospace;font-size:14px;line-height:1.42857;color:rgb(51,51);background:rgb(47,54,64);border:0px !important;"><ol class="linenums" style="border:0px;color:rgb(101,109,120);"><li class="L0" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,'Courier New',monospace;color:inherit;background-color:transparent;border:0px;">def spamrun(fn):<li class="L1" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"> sayspam(args):<li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> print("spam,spam,spam")<li class="L3" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> fn)<li class="L4" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,233);">return sayspam<li class="L5" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;">@spamrun<li class="L6" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> usefula,b):<li class="L7" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);">)<li class="L8" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"><li class="L9" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,233);">if name == "main"<li class="L0" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> useful(25) 运行结果

<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,237);">spamspam<li class="L1" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">10函数useful本身应该只是打印<code style="font-family:Menlo,monospace;font-size:14.4px;color:rgb(199,37,78);background-color:rgb(249,242,244);border:0px;">10，可是为什么最后的结果是这样的呢，其实我们可以简单的把这个代码理解为

<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"><li class="L6" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> useful =useful)<li class="L1" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);">)<h3 style="font-family:'-apple-system',47);font-size:18px;border:0px;">不带参数的多次使用<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,237);"> spamrun1 sayspam1):<li class="L8" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,84);">"spam1,spam1,spam1")<li class="L9" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);">)<li class="L0" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> sayspam1<li class="L1" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"><li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">@spamrun<li class="L3" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">@spamrun1<li class="L4" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);">):<li class="L5" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);">)<li class="L6" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"><li class="L7" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,84);">"main"<li class="L8" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);">spam1spam1<li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,sans-serif;font-size:16px;">这个代码理解为

<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,84);">"main"<li class="L1" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);">spamrun))<li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,47);font-size:18px;border:0px;">带参数的单次使用<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,237);"> attrs(kwds decorateffor k in kwds:<li class="L3" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> setattr k[k])<li class="L4" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> f<li class="L5" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> decorate<li class="L7" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"><li class="L8" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">@attrsversionadded="2.2"<code style="font-family:Menlo,237);"> author"Guido van Rossum" mymethodgetattrmymethod'versionadded'0'author'))<li class="L3" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"><li class="L5" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,84);">"main"<li class="L6" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">2.2<li class="L1" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;">Guido van Rossum<li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">2 mymethod <code style="font-family:Menlo,237);"> author"Guido van Rossum).(mymethod)<li class="L3" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"> mymethod(2)<h3 style="font-family:'-apple-system',47);font-size:18px;border:0px;">带参数的多次使用这次我们来看一个比较实际的例子，检查我们函数的输入输出是否符合我们的标准，比如我们希望的输入是（int，（int，float））输出是（int，float），这个例子在官网里有，但是在3.6版本中使用有些问题，这里进行了一些改动，如果要进一步了解可以看下functionTool。
<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,237);"> acceptstypes check_accepts new_f ):<li class="L3" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> assert lenlen+)),237);"> <li class="L4" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> "args cnt %d does not match %d"%),237);">))<li class="L5" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> t zip types):<li class="L6" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> isinstance <li class="L7" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> "arg %r does not match %s" f<li class="L0" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> update_wrappernew_f new_f<li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,monospace;color:inherit;background-color:transparent;border:0px;"><li class="L3" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> check_accepts<li class="L4" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> returnsrtype check_returns result result rtype <li class="L0" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,84);">"return value %r does not match %s" result<li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> new_f<li class="L5" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> check_returns<li class="L7" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">@accepts(intfloat))<li class="L9" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,236);">@returns(())<li class="L0" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> funcarg1 arg2 arg1 arg2 <li class="L2" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,84);">"main"<li class="L4" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> a 1'b')<li class="L5" style="border:0px;list-style:decimal;"><code style="font-family:Menlo,237);"> 这里故意输入了错误的参数，所以运行结果将我们的断言打印了出来

<pre class="prettyprint linenums prettyprinted" style="overflow:auto;font-family:Menlo,233);">AssertionError: arg 'b' does not match (<class'int'>,237);"><'float'>) func )).(accepts)说到这里，大家不难看出其实我们可以使用Decorators做很多工作，简化代码，使逻辑更清晰等。还有更多的用法等着大家自己去挖掘了，这里只简单的介绍了针对函数的用法，其实还可以针对class使用，具体的大家自己看看官方介绍，结合这篇文档应该就不难理解了。

转自：http://www.jcodecraeer.com/a/chengxusheji/chengxuyuan/2017/0418/7842.html

【Python】Python中的注解“@”

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