https://nalar.dev/tags/dataclasses/ Recent content in Dataclasses on Nalar Hugo en-us Tue, 01 Sep 2026 00:00:00 +0700 https://nalar.dev/design-value-objects-with-python-dataclasses/ Tue, 01 Sep 2026 00:00:00 +0700 https://nalar.dev/design-value-objects-with-python-dataclasses/ <p>Python dictionaries are convenient for passing a few values around, but they become fragile when a value has invariants or behavior that deserves a name. <code>dataclasses</code> can express small domain value objects without repetitive constructors and representation methods.</p> <h2 id="start-with-domain-meaning">Start with domain meaning</h2> <p>A price represented as a dictionary is easy to misuse:</p> <div x-data="{ code: $el.querySelector('code').innerText, copied: false }" class="code-block group relative my-6 overflow-hidden rounded-xl border border-line bg-surface-muted dark:border-night-line dark:bg-night-surface"> <button type="button" @click="navigator.clipboard.writeText(code); copied = true; setTimeout(() => copied = false, 1600)" class="absolute right-3 top-3 z-10 rounded-lg border border-line-strong bg-surface px-2 py-1 font-mono text-[0.65rem] text-muted opacity-0 transition group-hover:opacity-100 hover:bg-ink hover:text-white dark:border-night-line dark:bg-night dark:text-night-muted dark:hover:bg-white dark:hover:text-ink"> <span x-text="copied ? 'Copied' : 'Copy'"></span> </button> <div class="overflow-x-auto p-4 text-sm leading-6 [&_pre]:!m-0 [&_pre]:!bg-transparent [&_pre]:!p-0 [&_code]:font-mono"> <div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-python" data-lang="python"><span style="display:flex;"><span>price = {<span style="font-style:italic">&#34;amount&#34;</span>: 1299, <span style="font-style:italic">&#34;currency&#34;</span>: <span style="font-style:italic">&#34;USD&#34;</span>}</span></span></code></pre></div> </div> </div> <p>Any caller can omit a key or accidentally mix cents and dollars. A value object makes the contract explicit:</p>