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Visit website Recent posts Updated on $DATE date python shaozk - python Zola2026-09-06T00:00:00+00:00https://shaozk.xyz/tags/python/atom.xml 令人困惑的 Python is 语法 2026-09-06T00:00:00+00:00 2026-09-06T00:00:00+00:00 shaozk https://shaozk.xyz/blog/023-the-confusing-python-is-syntax/ <p>我们知道 Python is 语法是用于判断两个变量是否指向同一个对象，也就是说 is 会在内存层面判断否完全相同，而不仅仅是判断值是否相等。</p> <p>但是...</p> <h2 id="li-wai-qing-kuang">例外情况</h2> <pre class="giallo z-code"><code data-lang="python"><span class="giallo-l"><span class="z-source">a</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 5</span></span> <span class="giallo-l"><span class="z-source">b</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 5</span></span> <span class="giallo-l"><span class="z-support z-function z-builtin z-python">print</span><span class="z-punctuation">(</span><span class="z-meta z-function-call z-arguments z-python">a</span><span class="z-keyword z-control z-flow z-python"> is</span><span class="z-meta z-function-call z-arguments z-python"> b</span><span class="z-punctuation">)</span></span></code></pre> <p>你可以自己尝试在终端输入一下，看一下结果是什么。</p> <p>答案是这段代码会打印 True，然而这似乎和 is 的定义不相符合：从语法上看 a 和 b 是两个独立的变量，且值都是不可变对象字面值常量，其内存地址应该是不一样的才对。</p> <p>这究竟是为什么呢？</p> <h2 id="kai-shi-ai">开始 AI</h2> <blockquote> <p>DeepSeek: CPython 的小整数缓存机制，本质上是 “用空间换时间” 的优化策略：预先创建一批高频使用的小整数对象，让它们在整个解释器生命周期内被共享，避免重复创建和销毁。 缓存范围：不对称的 [-5, 256]</p> </blockquote> <p>本地测试确实是如此，在 -5 到 256 的左闭右闭区间内的整数，都会产生上文提到的例外情况。而只要超出这个范围，就变“正常”了。</p> <p>问题找到答案了，这是 Python 实现机制上的一个技巧，只要记住这个特性就好了。但结果真的是这样吗？</p> <h2 id="yuan-ma-zhi-qian-liao-wu-mi-mi">源码之前，了无秘密</h2> <p>为了加深映像，我决定查看一下 CPython 的源码实现。</p> <pre class="giallo z-code"><code data-lang="c"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// https://github.com/python/cpython/blob/main/Include/internal/pycore_runtime_structs.h</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#define</span><span class="z-entity z-name z-function"> _PY_NSMALLPOSINTS</span><span class="z-constant z-numeric"> 1025</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#define</span><span class="z-entity z-name z-function"> _PY_NSMALLNEGINTS</span><span class="z-constant z-numeric"> 5</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-source"> _Py_static_objects </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> struct</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> /* Small integers are preallocated in this array so that they</span></span> <span class="giallo-l"><span class="z-comment"> * can be shared.</span></span> <span class="giallo-l"><span class="z-comment"> * The integers that are preallocated are those in the range</span></span> <span class="giallo-l"><span class="z-comment"> * -_PY_NSMALLNEGINTS (inclusive) to _PY_NSMALLPOSINTS (exclusive).</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment"> */</span></span> <span class="giallo-l"><span class="z-source"> PyLongObject small_ints</span><span class="z-punctuation">[</span><span class="z-source">_PY_NSMALLNEGINTS </span><span class="z-keyword z-operator">+</span><span class="z-source"> _PY_NSMALLPOSINTS</span><span class="z-punctuation">];</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> /* ... */</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> singletons</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#define</span><span class="z-entity z-name z-function"> _Py_GLOBAL_OBJECT</span><span class="z-punctuation">(</span><span class="z-variable z-parameter">NAME</span><span class="z-punctuation">)</span><span class="z-constant z-character z-escape"> \</span></span> <span class="giallo-l"><span class="z-source"> _PyRuntime</span><span class="z-punctuation">.</span><span class="z-source">static_objects</span><span class="z-punctuation">.</span><span class="z-source">NAME</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#define</span><span class="z-entity z-name z-function"> _Py_SINGLETON</span><span class="z-punctuation">(</span><span class="z-variable z-parameter">NAME</span><span class="z-punctuation">)</span><span class="z-constant z-character z-escape"> \</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> _Py_GLOBAL_OBJECT</span><span class="z-punctuation">(</span><span class="z-source">singletons</span><span class="z-punctuation">.</span><span class="z-source">NAME</span><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#define</span><span class="z-entity z-name z-function"> _PyLong_SMALL_INTS _Py_SINGLETON</span><span class="z-punctuation">(</span><span class="z-source">small_ints</span><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier">static</span><span class="z-source"> PyObject </span><span class="z-keyword z-operator">*</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">get_small_int</span><span class="z-punctuation">(</span><span class="z-source">sdigit </span><span class="z-variable z-parameter">ival</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> assert</span><span class="z-punctuation">(</span><span class="z-entity z-name z-function">IS_SMALL_INT</span><span class="z-punctuation">(</span><span class="z-source">ival</span><span class="z-punctuation">));</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-punctuation"> (</span><span class="z-source">PyObject </span><span class="z-keyword z-operator">*</span><span class="z-punctuation">)</span><span class="z-keyword z-operator">&amp;</span><span class="z-source">_PyLong_SMALL_INTS</span><span class="z-punctuation">[</span><span class="z-source">_PY_NSMALLNEGINTS </span><span class="z-keyword z-operator">+</span><span class="z-source"> ival</span><span class="z-punctuation">];</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span></code></pre> <p>可以看到当值为小整数时，会直接通过 ival + 5 从预先分配好的数组中拿取数据，这也就是小整数共享内存的原因。</p> <h2 id="gen-ai-shuo-de-you-dian-bu-yi-yang">跟 AI 说的有点不一样？</h2> <p>等等，为啥上限值是 1025 而不是 257？最新的 CPython 已经准备将小整数范围修改为 [-5, 1024] 了。</p> <blockquote> <p>Gemini Python 3.13（当前稳定版） / Python 3.14（即将发布）：没有包含此修改。它们的 _PY_NSMALLPOSINTS 依然是旧的 257，小整数池仍为 [-5, 256]。 Python 3.15（开发中版本）：已纳入。这个修改直接合并在 main 开发分支上。按照 Python 每年一个次要版本的发布节奏，包含此变动的 Python 3.15 正式版预计将于 2026 年 10 月左右发布。</p> </blockquote> <p>现在的时间是 2026 年 9 月 14 号，如果我不去看看源码的话，我想很难知道最新的情况。</p> <h2 id="ru-he-bi-mian">如何避免</h2> <p>在判断值是否相等的时候不使用 is，而是使用 ==（也应该这么做）。</p> <h2 id="ling-wai-de-yi-chong-qing-kuang">另外的一种情况</h2> <pre class="giallo z-code"><code data-lang="python"><span class="giallo-l"><span class="z-source">a</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-language z-python"> True</span></span> <span class="giallo-l"><span class="z-source">b</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-language z-python"> True</span></span> <span class="giallo-l"><span class="z-support z-function z-builtin z-python">print</span><span class="z-punctuation">(</span><span class="z-meta z-function-call z-arguments z-python">a</span><span class="z-keyword z-control z-flow z-python"> is</span><span class="z-meta z-function-call z-arguments z-python"> b</span><span class="z-punctuation">)</span></span></code></pre> <p>其答案也是 True，看上去（表现）和小整数一样，但其底层原理却不相同，这里不展开。</p> <h2 id="can-kao">参考</h2> <ul> <li><a rel="external" href="https://zackoverflow.dev/writing/how-often-does-python-allocate">How often does Python allocate?</a></li> </ul> 添加 Python 应用到 Homebrew 2026-08-05T00:00:00+00:00 2026-08-05T00:00:00+00:00 shaozk https://shaozk.xyz/blog/016-adding-python-application-to-homebrew/ <p>最近看到开源工具 <a rel="external" href="https://github.com/Maciek-roboblog/Claude-Code-Usage-Monitor">claude-monitor</a> 的一个 <a rel="external" href="https://github.com/Maciek-roboblog/Claude-Code-Usage-Monitor/issues/31">issue</a>，目的是希望给工具增加 brew 管理，我想着没事做就尝试了一下。claude-monitor 是一个 Python 应用，是符合 brew 管理<a rel="external" href="https://docs.brew.sh/Language-Specific-Formulae">前提</a>的。</p> <p>不过最终我只在本地完成了测试，没正式往官方提交 PR，只是将生成的 Formula 放在 issue 的评论中（也算是为开源做了贡献吧）。</p> <h1 id="qian-ti-zhi-shi">前提知识</h1> <p><a rel="external" href="https://brew.sh/">Homebrew</a> 是一个 MacOS 常用的开源包管理工具，简称 brew。提供将自己应用添加进 brew 管理的功能，完成后用户就可以直接用 <code>brew install &lt;包名&gt;</code> 下载你的工具了。</p> <p><a rel="external" href="https://docs.brew.sh/Formula-Cookbook#homebrew-terminology">Formula</a> 可以理解为 brew 定义包的方式，你需要为你的应用生成一个专有的 Formula，之后提交 PR 到 <a rel="external" href="https://github.com/Homebrew/brew">brew 的仓库</a>中去，等待管理人员审阅。</p> <h1 id="cao-zuo-bu-zou">操作步骤</h1> <p>使用 <code>brew create</code> 命令，参数为你在 GitHub 上打包好的源码包 URL，另外增加 <code>--python</code> 选项代表指定生成 python 的 Fromula：</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">brew</span><span class="z-string"> create --python https://github.com/Maciek-roboblog/Claude-Code-Usage-Monitor/archive/refs/tags/v4.0.0.tar.gz</span></span></code></pre> <p>执行完输入你的包名：</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">Formula</span><span class="z-string"> name</span><span class="z-source"> [Claude-Code-Usage-Monitor]: claude-monitor</span></span></code></pre> <p>生成对应的 Formula 文件，其绝对路径为：<code>/opt/homebrew/Library/Taps/homebrew/homebrew-core/Formula/c/claude-monitor.rb</code>。内容如下：</p> <pre class="giallo z-code"><code data-lang="ruby"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># Documentation: https://docs.brew.sh/Formula-Cookbook</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># https://docs.brew.sh/rubydoc/Formula</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># PLEASE REMOVE ALL GENERATED COMMENTS BEFORE SUBMITTING YOUR PULL REQUEST!</span></span> <span class="giallo-l"><span class="z-keyword">class</span><span class="z-entity z-name z-type"> ClaudeMonitor</span><span class="z-punctuation"> &lt;</span><span class="z-entity z-other z-inherited-class"> Formula</span></span> <span class="giallo-l"><span class="z-keyword"> include</span><span class="z-support z-class"> Language</span><span class="z-punctuation">::</span><span class="z-support z-class">Python</span><span class="z-punctuation">::</span><span class="z-variable z-other z-constant">Virtualenv</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source"> desc </span><span class="z-punctuation z-definition z-string z-string">&quot;Real-time Claude Code usage monitor with predictions and warnings&quot;</span></span> <span class="giallo-l"><span class="z-source"> homepage 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do</span></span> <span class="giallo-l"><span class="z-source"> url </span><span class="z-punctuation z-definition z-string z-string">&quot;https://files.pythonhosted.org/packages/34/74/c6428f875774288bec1396f5bfcbc2d925700a4dad61727fd5f2b12f249d/wcwidth-0.8.2.tar.gz&quot;</span></span> <span class="giallo-l"><span class="z-source"> sha256 </span><span class="z-punctuation z-definition z-string z-string">&quot;91fbef97204b96a3d4d421609b80340b760cf33e26da123ff243d76b1fda8dda&quot;</span></span> <span class="giallo-l"><span class="z-keyword"> end</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword"> def</span><span class="z-entity z-name z-function"> install</span></span> <span class="giallo-l"><span class="z-variable z-other z-constant"> ENV</span><span class="z-source">[</span><span class="z-punctuation z-definition z-string z-string">&quot;CARGO_NET_GIT_FETCH_WITH_CLI&quot;</span><span class="z-source">]</span><span class="z-keyword z-operator"> =</span><span class="z-punctuation z-definition z-string z-string"> &quot;true&quot;</span></span> <span class="giallo-l"><span class="z-variable z-other z-constant"> ENV</span><span class="z-source">[</span><span class="z-punctuation z-definition z-string z-string">&quot;MATURIN_PEP517&quot;</span><span class="z-source">]</span><span class="z-keyword z-operator"> =</span><span class="z-punctuation z-definition z-string z-string"> &quot;1&quot;</span></span> <span class="giallo-l"><span class="z-source"> virtualenv_install_with_resources</span></span> <span class="giallo-l"><span class="z-keyword"> end</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-support z-function"> test</span><span class="z-keyword"> do</span></span> <span class="giallo-l"><span class="z-support z-function"> system</span><span class="z-source"> bin</span><span class="z-keyword z-operator">/</span><span class="z-punctuation z-definition z-string z-string">&quot;claude-monitor&quot;</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;--version&quot;</span></span> <span class="giallo-l"><span class="z-keyword"> end</span></span> <span class="giallo-l"><span class="z-keyword">end</span></span> <span class="giallo-l"></span></code></pre> <p>然后按照下面三个命令完成本地测试就可以了，整个过程还是比较简单的。</p> <pre class="giallo z-code"><code data-lang="ruby"><span class="giallo-l"><span class="z-variable z-other z-constant">Please</span><span class="z-source"> audit </span><span class="z-keyword z-operator">and</span><span class="z-support z-function"> test</span><span class="z-source"> formula before </span><span class="z-constant z-language">submitting</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-variable z-other z-constant"> HOMEBREW_NO_INSTALL_FROM_API</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric">1</span><span class="z-source"> brew audit </span><span class="z-keyword z-operator">--</span><span class="z-keyword">new</span><span class="z-source"> claude</span><span class="z-keyword z-operator">-</span><span class="z-source">monitor</span></span> <span class="giallo-l"><span class="z-variable z-other z-constant"> HOMEBREW_NO_INSTALL_FROM_API</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric">1</span><span class="z-source"> brew install </span><span class="z-keyword z-operator">--</span><span class="z-source">build</span><span class="z-keyword z-operator">-</span><span class="z-source">from</span><span class="z-keyword z-operator">-</span><span class="z-source">source </span><span class="z-keyword z-operator">--</span><span class="z-source">verbose </span><span class="z-keyword z-operator">--</span><span class="z-source">debug claude</span><span class="z-keyword z-operator">-</span><span class="z-source">monitor</span></span> <span class="giallo-l"><span class="z-variable z-other z-constant"> HOMEBREW_NO_INSTALL_FROM_API</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric">1</span><span class="z-source"> brew </span><span class="z-support z-function">test</span><span class="z-source"> claude</span><span class="z-keyword z-operator">-</span><span class="z-source">monitor</span></span></code></pre> <p>Done!</p> Python 可变默认参数陷阱 2026-07-07T00:00:00+00:00 2026-07-07T00:00:00+00:00 shaozk https://shaozk.xyz/blog/005-function-mutable-default-arg/ <blockquote> <p>无意中刷到的「码农高天」的 Python 视频，尝试一下自己也踩坑了。</p> </blockquote> <p>示例代码如下：</p> <pre class="giallo z-code"><code data-lang="python"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Player</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type z-function z-python"> def</span><span class="z-support z-function z-magic z-python"> __init__</span><span class="z-punctuation">(</span><span class="z-variable z-parameter z-function z-language z-special z-self z-python">self</span><span class="z-punctuation">,</span><span class="z-variable z-parameter"> name</span><span class="z-punctuation">:</span><span class="z-support z-type z-python"> str</span><span class="z-punctuation">,</span><span class="z-variable z-parameter"> items</span><span class="z-punctuation">:</span><span class="z-support z-type z-python"> list</span><span class="z-keyword z-operator"> =</span><span class="z-punctuation"> []):</span></span> <span class="giallo-l"><span class="z-variable z-language z-special z-self z-python"> self</span><span class="z-punctuation">.</span><span class="z-source">name</span><span class="z-keyword z-operator"> =</span><span class="z-source"> name</span></span> <span class="giallo-l"><span class="z-variable z-language z-special z-self z-python"> self</span><span class="z-punctuation">.</span><span class="z-source">items</span><span class="z-keyword z-operator"> =</span><span class="z-source"> items</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">a</span><span class="z-keyword z-operator"> =</span><span class="z-meta z-function-call z-python"> Player</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;A&quot;</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source">b</span><span class="z-keyword z-operator"> =</span><span class="z-meta z-function-call z-python"> Player</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;B&quot;</span><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">a</span><span class="z-punctuation">.</span><span class="z-source">items</span><span class="z-punctuation">.</span><span class="z-meta z-function-call z-python">append</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;hello&quot;</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source">b</span><span class="z-punctuation">.</span><span class="z-source">items</span><span class="z-punctuation">.</span><span class="z-meta z-function-call z-python">append</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;world&quot;</span><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-support z-function z-builtin z-python">print</span><span class="z-punctuation">(</span><span class="z-meta z-function-call z-arguments z-python">a</span><span class="z-punctuation">.</span><span class="z-meta z-function-call z-arguments z-python">items</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-support z-function z-builtin z-python">print</span><span class="z-punctuation">(</span><span class="z-meta z-function-call z-arguments z-python">b</span><span class="z-punctuation">.</span><span class="z-meta z-function-call z-arguments z-python">items</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> </span></span></code></pre> <p>请问终端打印结果是什么？</p> <p>我下意识给出的答案，包括身边的朋友也是：</p> <pre class="giallo z-code"><code data-lang="plain"><span class="giallo-l"><span>[&#39;hello&#39;]</span></span> <span class="giallo-l"><span>[&#39;world&#39;]</span></span></code></pre> <p>而正确的答案是：</p> <pre class="giallo z-code"><code data-lang="plain"><span class="giallo-l"><span>[&#39;hello&#39;, &#39;world&#39;]</span></span> <span class="giallo-l"><span>[&#39;hello&#39;, &#39;world&#39;]</span></span></code></pre> <p>什么原理？</p> <p>Python 中函数的默认参数，只会被创建一次。也就是说所有使用该默认参数的函数调用，都会共享这个默认值。</p> <p>如果参数是不可变的，这没有影响。但如果参数可变（mutable），那就会掉进如上这类陷阱。</p> <p>修复方法比较简单，将默认参数 <code>[]</code> 修改为 <code>None</code> 。</p> <pre class="giallo z-code"><code data-lang="python"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Player</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type z-function z-python"> def</span><span class="z-support z-function z-magic z-python"> __init__</span><span class="z-punctuation">(</span><span class="z-variable z-parameter z-function z-language z-special z-self z-python">self</span><span class="z-punctuation">,</span><span class="z-variable z-parameter"> name</span><span class="z-punctuation">:</span><span class="z-support z-type z-python"> str</span><span class="z-punctuation">,</span><span class="z-variable z-parameter"> items</span><span class="z-punctuation">:</span><span class="z-support z-type z-python"> list</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-language z-python"> None</span><span class="z-punctuation">):</span></span> <span class="giallo-l"><span class="z-variable z-language z-special z-self z-python"> self</span><span class="z-punctuation">.</span><span class="z-source">name</span><span class="z-keyword z-operator"> =</span><span class="z-source"> name</span></span> <span class="giallo-l"><span class="z-keyword z-control z-flow z-python"> if</span><span class="z-source"> items</span><span class="z-keyword z-operator z-logical z-python"> is</span><span class="z-constant z-language z-python"> None</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-variable z-language z-special z-self z-python"> self</span><span class="z-punctuation">.</span><span class="z-source">items</span><span class="z-keyword z-operator"> =</span><span class="z-punctuation"> []</span></span> <span class="giallo-l"><span class="z-keyword z-control z-flow z-python"> else</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-variable z-language z-special z-self z-python"> self</span><span class="z-punctuation">.</span><span class="z-source">items</span><span class="z-keyword z-operator"> =</span><span class="z-source"> items</span></span></code></pre> <p>那么为什么要这样设计呢？</p> <ol> <li>一次创建，多次使用。减少创建重复的对象，提高性能</li> <li>提供类似静态变量功能，保持状态</li> </ol> <p><a rel="external" href="https://www.bilibili.com/video/BV1NP4y1g7CT?vd_source=c879317db216a66b04538be69b7cc5b5">video</a></p>