Python奇技淫巧（1）_编程语言论坛

Python奇技淫巧（1）

课课家iOS游客发布于 2018-04-08 09:09查看:1135

显示有限的接口到外部

当发布python第三方package时, 并不希望代码中所有的函数或者class可以被外部import, 在__init__.py中添加__all__属性,
该list中填写可以import的类或者函数名, 可以起到限制的import的作用, 防止外部import其他函数或者类

with的魔力

with语句需要支持上下文管理协议的对象, 上下文管理协议包含 __enter__ 和 __exit__ 两个方法. with语句建立运行时上下文需要通过这两个方法执行进入和退出操作.

其中上下文表达式是跟在with之后的表达式, 该表示大返回一个上下文管理对象

详细原理可以查看这篇文章《》

知道具体原理, 我们可以自定义支持上下文管理协议的类, 类中实现 __enter__ 和 __exit__ 方法

执行结果如下:

证明了会先执行 __enter__ 方法, 然后调用with内的逻辑, 最后执行 __exit__ 做退出处理, 并且, 即使出现异常也能正常退出

filter的用法

相对filter而言, map和reduce使用的会更频繁一些, filter正如其名字, 按照某种规则过滤掉一些元素

一行作判断

当条件满足时, 返回的为等号后面的变量, 否则返回else后语句

装饰器之单例

使用装饰器实现简单的单例模式

staticmethod装饰器

类中两种常用的装饰, 首先区分一下他们

普通成员函数, 其中第一个隐式参数为对象
classmethod装饰器, 类方法(给人感觉非常类似于OC中的类方法), 其中第一个隐式参数为类
staticmethod装饰器, 没有任何隐式参数. python中的静态方法类似与C++中的静态方法

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<p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">显示有限的接口到外部<p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">当发布python第三方package时, 并不希望代码中所有的函数或者class可以被外部import, 在<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">__init__.py</code>中添加<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">__all__</code>属性, 该list中填写可以import的类或者函数名, 可以起到限制的import的作用, 防止外部import其他函数或者类<img src="/Public/forum/ueditor/image/20180408/1523149403473256.png" title="1523149403473256.png" alt="image.png"/><h2 id="with的魔力" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 24px; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 36px; font-family: "Microsoft YaHei", "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">with的魔力</h2><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">with语句需要支持<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">上下文管理协议的对象</code>, 上下文管理协议包含 <span id="crayon-5ac95d1bb3a7b731630560" class="crayon-syntax crayon-syntax-inline crayon-theme-github crayon-theme-github-inline crayon-font-monaco" style="margin-top: 0px; margin-right: 2px; margin-left: 2px; padding: 0px 2px; box-sizing: border-box; text-size-adjust: none; width: auto; font-family: Monaco, MonacoRegular, "Courier New", monospace; border: 1px solid rgb(222, 222, 222) !important; margin-bottom: 25px !important; font-size: 13px !important; overflow: hidden !important; position: relative !important; direction: ltr !important; background-color: rgb(248, 248, 255) !important; line-height: 15px !important;"><span class="crayon-pre crayon-code" style="margin: 0px; padding-right: 0px; padding-left: 0px; width: auto; color: rgb(0, 0, 0); overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; background: none !important; line-height: 15px !important;"><span class="crayon-v" style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">__enter__ 和 <span id="crayon-5ac95d1bb3a7f106394580" class="crayon-syntax crayon-syntax-inline crayon-theme-github crayon-theme-github-inline crayon-font-monaco" style="margin-top: 0px; margin-right: 2px; margin-left: 2px; padding: 0px 2px; box-sizing: border-box; text-size-adjust: none; width: auto; font-family: Monaco, MonacoRegular, "Courier New", monospace; border: 1px solid rgb(222, 222, 222) !important; margin-bottom: 25px !important; font-size: 13px !important; overflow: hidden !important; position: relative !important; direction: ltr !important; background-color: rgb(248, 248, 255) !important; line-height: 15px !important;"><span class="crayon-pre crayon-code" style="margin: 0px; padding-right: 0px; padding-left: 0px; width: auto; color: rgb(0, 0, 0); overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; background: none !important; line-height: 15px !important;"><span class="crayon-v" style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">__exit__ 两个方法. with语句建立运行时上下文需要通过这两个方法执行<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">进入和退出</code>操作.<p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">其中<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">上下文表达式</code>是跟在with之后的表达式, 该表示大返回一个上下文管理对象<img src="/Public/forum/ueditor/image/20180408/1523149449652519.png" title="1523149449652519.png" alt="image.png"/><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">详细原理可以查看这篇文章《》<p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">知道具体原理, 我们可以自定义支持上下文管理协议的类, 类中实现 <span id="crayon-5ac95d1bb3a86649574072" class="crayon-syntax crayon-syntax-inline crayon-theme-github crayon-theme-github-inline crayon-font-monaco" style="margin-top: 0px; margin-right: 2px; margin-left: 2px; padding: 0px 2px; box-sizing: border-box; text-size-adjust: none; width: auto; font-family: Monaco, MonacoRegular, "Courier New", monospace; border: 1px solid rgb(222, 222, 222) !important; margin-bottom: 25px !important; font-size: 13px !important; overflow: hidden !important; position: relative !important; direction: ltr !important; background-color: rgb(248, 248, 255) !important; line-height: 15px !important;"><span class="crayon-pre crayon-code" style="margin: 0px; padding-right: 0px; padding-left: 0px; width: auto; color: rgb(0, 0, 0); overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; background: none !important; line-height: 15px !important;"><span class="crayon-v" style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">__enter__ 和 <span id="crayon-5ac95d1bb3a89512907618" class="crayon-syntax crayon-syntax-inline crayon-theme-github crayon-theme-github-inline crayon-font-monaco" style="margin-top: 0px; margin-right: 2px; margin-left: 2px; padding: 0px 2px; box-sizing: border-box; text-size-adjust: none; width: auto; font-family: Monaco, MonacoRegular, "Courier New", monospace; border: 1px solid rgb(222, 222, 222) !important; margin-bottom: 25px !important; font-size: 13px !important; overflow: hidden !important; position: relative !important; direction: ltr !important; background-color: rgb(248, 248, 255) !important; line-height: 15px !important;"><span class="crayon-pre crayon-code" style="margin: 0px; padding-right: 0px; padding-left: 0px; width: auto; color: rgb(0, 0, 0); overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; background: none !important; line-height: 15px !important;"><span class="crayon-v" style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">__exit__ 方法<img src="/Public/forum/ueditor/image/20180408/1523149569231966.png" title="1523149569231966.png" alt="image.png"/>执行结果如下:<img src="/Public/forum/ueditor/image/20180408/1523149608998780.png" title="1523149608998780.png" alt="image.png"/>证明了会先执行 <span id="crayon-5ac95d1bb3a98448057054" class="crayon-syntax crayon-syntax-inline crayon-theme-github crayon-theme-github-inline crayon-font-monaco" style="margin-top: 0px; margin-right: 2px; margin-left: 2px; padding: 0px 2px; box-sizing: border-box; text-size-adjust: none; width: auto; font-family: Monaco, MonacoRegular, "Courier New", monospace; color: rgb(94, 94, 94); border: 1px solid rgb(222, 222, 222) !important; margin-bottom: 25px !important; font-size: 13px !important; overflow: hidden !important; position: relative !important; direction: ltr !important; background-color: rgb(248, 248, 255) !important; line-height: 15px !important;"><span class="crayon-pre crayon-code" style="margin: 0px; padding-right: 0px; padding-left: 0px; width: auto; color: rgb(0, 0, 0); overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; background: none !important; line-height: 15px !important;"><span class="crayon-v" style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">__enter__ 方法, 然后调用with内的逻辑, 最后执行 <span id="crayon-5ac95d1bb3a9b706160042" class="crayon-syntax crayon-syntax-inline crayon-theme-github crayon-theme-github-inline crayon-font-monaco" style="margin-top: 0px; margin-right: 2px; margin-left: 2px; padding: 0px 2px; box-sizing: border-box; text-size-adjust: none; width: auto; font-family: Monaco, MonacoRegular, "Courier New", monospace; color: rgb(94, 94, 94); border: 1px solid rgb(222, 222, 222) !important; margin-bottom: 25px !important; font-size: 13px !important; overflow: hidden !important; position: relative !important; direction: ltr !important; background-color: rgb(248, 248, 255) !important; line-height: 15px !important;"><span class="crayon-pre crayon-code" style="margin: 0px; padding-right: 0px; padding-left: 0px; width: auto; color: rgb(0, 0, 0); overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; background: none !important; line-height: 15px !important;"><span class="crayon-v" style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">__exit__ 做退出处理, 并且, 即使出现异常也能正常退出<h2 id="filter的用法" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 24px; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 36px; font-family: "Microsoft YaHei", "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">filter的用法</h2><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">相对<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">filter</code>而言, map和reduce使用的会更频繁一些, <code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">filter</code>正如其名字, 按照某种规则<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">过滤</code>掉一些元素<img src="/Public/forum/ueditor/image/20180408/1523149628893095.png" title="1523149628893095.png" alt="image.png"/><h2 id="一行作判断" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 24px; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 36px; font-family: "Microsoft YaHei", "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">一行作判断</h2><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">当条件满足时, 返回的为等号后面的变量, 否则返回else后语句<img src="/Public/forum/ueditor/image/20180408/1523149640549541.png" title="1523149640549541.png" alt="image.png"/><h2 id="装饰器之单例" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 24px; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 36px; font-family: "Microsoft YaHei", "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">装饰器之单例</h2><blockquote style="border-width: 0px 0px 0px 5px; border-top-style: initial; border-right-style: initial; border-bottom-style: initial; border-left-style: solid; border-top-color: initial; border-right-color: initial; border-bottom-color: initial; border-left-color: rgb(238, 238, 238); border-image: initial; margin: 0px 0px 10px; padding: 10px 20px; font-size: 15px; color: rgb(94, 94, 94); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">使用装饰器实现简单的单例模式</blockquote><img src="/Public/forum/ueditor/image/20180408/1523149669515872.png" title="1523149669515872.png" alt="image.png"/><h2 id="staticmethod装饰器" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 24px; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 36px; font-family: "Microsoft YaHei", "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">staticmethod装饰器</h2><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">类中两种常用的装饰, 首先区分一下他们<ul style="border: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; list-style-position: outside; list-style-image: initial; color: rgb(46, 46, 46); font-family: "Microsoft YaHei", 宋体, "Myriad Pro", Lato, "Helvetica Neue", Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);" class=" list-paddingleft-2"><li>普通成员函数, 其中第一个隐式参数为<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">对象</code></li><li><code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">classmethod装饰器</code>, 类方法(给人感觉非常类似于OC中的类方法), 其中第一个隐式参数为<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">类</code></li><li><code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">staticmethod装饰器</code>, 没有任何隐式参数. <code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;">python中的静态方法类似与C++中的静态方法</code></li><li><code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;"><img src="/Public/forum/ueditor/image/20180408/1523149725352061.png" title="1523149725352061.png" alt="image.png"/></code></li><li><code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace;"></code></li></ul>
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Python奇技淫巧（1）

with的魔力

filter的用法

一行作判断

装饰器之单例

staticmethod装饰器

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Python奇技淫巧 （1）

with的魔力

filter的用法

一行作判断

装饰器之单例

staticmethod装饰器

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