post: fastapi lifespan & js coding style

Author: Starslayerx

content/posts/2025-10-23_morden-js-code-quailty.md

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++++
+date = '2025-10-23T8:00:00+08:00'
+draft = false   
+title = 'Code Quailty'
+tags = ['Javascript']
++++
+
+### 3.1 Debugging in the browser
+
+Debugging is the process of finding and fixing errors with a script.
+All morden browsers and most other environments support debugging tools - a special UI in developer tools that makes debugging much easier.
+It also allows to trace the code step by step to see what exactly is going on.
+
+#### The "Sources" panel
+
+The Sources panel has 3 parts:
+
+1. The **File Navigator** pane lists HTML, Javascript, CSS and other files, including images that are attatched to the page. Chrome extensions may appera here too.
+2. The **Code Editor** pane shows the source code.
+3. The **Javascript Debugging** pane is for debugging, we'll explore it soon.
+
+#### Console
+
+按 `Esc` 可以打开控制台，在其中可以输入命令，按回车执行。
+
+#### Breakpoints
+
+点击代码行号部分添加检查点，可以用于调试代码，暂停代码的执行。
+
+也可以使用 `debuugger` 命令来暂停代码
+
+```Javascript
+function hello(name) {
+    let prase = 'Hello, ${name}!';
+
+    debugger;
+
+    say(prase);
+}
+```
+
+#### Pause and look around
+
+代码框右侧有 3 个部分：
+
+1. **`Watch` - shows current values for any expressions.**  
+   监控表达式，该部分实时显示某个表达式的值
+
+2. **`Call Stack` - shows the nested calls chain**  
+   调用栈，显示当前执行位置的 “函数调用轨迹”
+
+3. **`Scope` - current variables**  
+   作用域，展示当前代码可访问的所有变量的地方
+   - Local: 当前函数内部局部变量
+   - Closure: 函数外层作用域闭包变量
+   - Global: 全局作用域变量
+   - this: 当前上下文绑定的对象
+
+#### Logging
+
+要在终端输出内容，使用 `console.log` 函数。
+例如输出 `0` 到 `4`：
+
+```Javascript
+for (let i = 0; i < 5; i++) {
+    console.log("value", i)
+}
+```

content/posts/2025-10-24_fastapi-lifespan-events.md

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+date = '2025-10-24T8:00:00+08:00'
+draft = false
+title = 'Fastapi Lifespan Events'
+tags = ['Fastapi']
++++
+
+## Lifespan Events
+
+通过生命周期事件可以定义在应用开启之前需要执行的代码，这意味着这些代码会在开始接收外部请求之前被执行一次。
+同样地，也可以定义应用在关闭的时候定义需要执行的代码，在尽力处理完所有请求后，该代码会被执行一次。
+
+这对于设置需要在整个 app 的请求间共享的资源时非常有用，或者是需要进行清理工作的时候。
+例如，一个数据库连接池，或者加载一个共享的机器学习模型。
+
+### Use Case
+
+下面通过一个例子说明如何使用。
+
+假如你有一个机器学习模型，并且需要让其处理请求，由于请求都共享同一个模型，因此不是一个请求对应一个模型，或一个用户一个模型。
+假设模型加载需要一定的时间，因为要从磁盘中读取大量的数据，因此不能每个请求都去加载一次。
+你可以在顶层的模块文件中定义加载，但这意味着当进行简单的自动化测试的时候，也会加载该模型，这样就会很慢。
+
+这就是需要解决的问题，需要在请求响应之前加载模型，也不是在代码被加载的时候加载模型。
+
+### Lifespan
+
+可以通过在 `FastAPI` app 中使用 `lifespan` 参数来定义启动和关闭逻辑，以及一个 "context manager" (上下文管理器)。
+
+通过下面这种方法创建一个含 `yield` 的 `function`
+
+```Python
+from contextlib import asynccontextmanager
+
+from fastapi impor FastAPI
+
+def fake_answer_to_everything_ml_model(x: float):
+    return x * 42
+
+ml_models = {}
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    # Load the ML model
+    ml_models["answer_to_everything"] = fake_answer_to_everything_ml_model
+    yield
+    # Clean up the ML models and release the resources
+    ml_models.clear()
+
+app = FastAPI(lifespan=lifespan)
+
+@app.get("/predict")
+async def predict(x: float):
+    result = ml_models["answer_to_everything"](x)
+    return {"result": result}
+```
+
+这里在生成器 `yield` 之前将模拟的昂贵函数放入机器学习字典中。
+这段代码将在应用程序接收请求之前执行，即启动阶段。
+
+然后，在 `yield` 后面，卸载模型。
+这段改名将在完成请求之后执行，即关闭之前，这样会释放内存和 CPU 资源。
+
+#### Lifespan function
+
+第一件注意到的事是，定义了一个带 `yield` 的 async function，这与带 `yield` 的 Dependencies 相同。
+
+```Python
+async def lifespan(app: FastAPI):
+    ...
+    yield
+    ...
+```
+
+在 `yield` 之前的部分会在应用开启之前执行，`yield` 之后的部分会在应用结束之后执行。
+
+#### Async Context Manager
+
+该函数使用 `@asynccontextmanager` 异步上下文管理器装饰，将函数转化成一个 "**async context manager**"。
+
+```
+from contextlib import asynccontextmanager
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    ...
+```
+
+在 Python 中的 **context manager** 上下文管理器可以在 `with` 语法中使用，例如 `open()` 可以作为上下文管理器使用：
+
+```Python
+with open("file.txt") as file:
+    file.read()
+```
+
+在最近的 Python 版本中，也有一个 **async context manager** 异步上下文管理器，可以通过 `async with` 使用：
+
+```Python
+async with lifespan(app):
+    await do_stuff()
+```
+
+当使用上面那样创建一个（异步）上下文管理器时，实际发生的事是。
+在进入 `with` 块之前，会去执行 `yield` 之前的代码，退出 `with` 块之后，再去执行 `yield` 之后的代码。
+
+在之前的例子中，并没有直接这样写，而是将其传递给 FastAPI 使用。
+
+`FastAPI` app 的 `lifespan` 参数接受一个 **async context manager**，因此可以直接将 `lifespan` 异步上下文管理器传递给它。
+
+```Python
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    ...
+    yield
+    ...
+
+app = FataAPI(lifespan=lifespan)
+```
+
+### Alternative Events (deprecated)
+
+旧的语法这里就不再详细介绍了，大概下面这样使用
+
+```Python
+@app.on_event("startup")
+async def startup():
+    print("启动xxx")
+
+@app.on_event("shutdown")
+async def shotdown():
+    print("关闭xxx")
+```
+
+### Technical Details
+
+在 ASGI 协议规范下，这是 [Lifespan Protocol](https://asgi.readthedocs.io/en/latest/specs/lifespan.html) 的一部分，并且定义了 `startup` 和 `shutdown` 的事件。
+
+要记住，这种 lifespan events 将只会在 mian application 执行，而不会在 [Sub Applications - Mounts](https://fastapi.tiangolo.com/advanced/sub-applications/) 中执行。

public/archives/index.html

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-posts</p></div></div><div class="ml-12 space-y-3"><article class="group bg-card border-border hover:bg-accent/50 rounded-lg border p-4 transition-all duration-300"><div class="flex items-center justify-between gap-4"><div class="min-w-0 flex-1"><h4 class="text-foreground group-hover:text-primary mb-3 font-medium transition-colors duration-200"><a href=/posts/understanding-svg-paths/ class=block>Understanding SVG Paths</a></h4><div class="text-muted-foreground flex items-center gap-4 text-xs"><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5A2 2 0 003 7v12a2 2 0 002 2z"/></svg>
+<span>58 posts total</span></div><div class="flex items-center gap-1"><svg class="h-4 w-4" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5A2 2 0 003 7v12a2 2 0 002 2z"/></svg>
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+posts</p></div></div><div class="relative mb-8"><div class="relative mb-4 flex items-center"><div class="bg-accent border-background absolute left-2 z-10 h-4 w-4 rounded-full border-2"></div><div class=ml-12><h3 class="text-foreground text-lg font-semibold">October 2025</h3><p class="text-muted-foreground text-xs">4
+posts</p></div></div><div class="ml-12 space-y-3"><article class="group bg-card border-border hover:bg-accent/50 rounded-lg border p-4 transition-all duration-300"><div class="flex items-center justify-between gap-4"><div class="min-w-0 flex-1"><h4 class="text-foreground group-hover:text-primary mb-3 font-medium transition-colors duration-200"><a href=/posts/fastapi-lifespan-events/ class=block>Fastapi Lifespan Events</a></h4><div class="text-muted-foreground flex items-center gap-4 text-xs"><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5A2 2 0 003 7v12a2 2 0 002 2z"/></svg>
+<time datetime=2025-10-24>10-24</time></div><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 8v4l3 3m6-3A9 9 0 113 12a9 9 0 0118 0z"/></svg>
+<span>3
+min</span></div></div></div></div></article><article class="group bg-card border-border hover:bg-accent/50 rounded-lg border p-4 transition-all duration-300"><div class="flex items-center justify-between gap-4"><div class="min-w-0 flex-1"><h4 class="text-foreground group-hover:text-primary mb-3 font-medium transition-colors duration-200"><a href=/posts/code-quailty/ class=block>Code Quailty</a></h4><div class="text-muted-foreground flex items-center gap-4 text-xs"><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5A2 2 0 003 7v12a2 2 0 002 2z"/></svg>
+<time datetime=2025-10-23>10-23</time></div><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 8v4l3 3m6-3A9 9 0 113 12a9 9 0 0118 0z"/></svg>
+<span>1
+min</span></div></div></div></div></article><article class="group bg-card border-border hover:bg-accent/50 rounded-lg border p-4 transition-all duration-300"><div class="flex items-center justify-between gap-4"><div class="min-w-0 flex-1"><h4 class="text-foreground group-hover:text-primary mb-3 font-medium transition-colors duration-200"><a href=/posts/understanding-svg-paths/ class=block>Understanding SVG Paths</a></h4><div class="text-muted-foreground flex items-center gap-4 text-xs"><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5A2 2 0 003 7v12a2 2 0 002 2z"/></svg>
 <time datetime=2025-10-22>10-22</time></div><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 8v4l3 3m6-3A9 9 0 113 12a9 9 0 0118 0z"/></svg>
 <span>8
 min</span></div></div></div></div></article><article class="group bg-card border-border hover:bg-accent/50 rounded-lg border p-4 transition-all duration-300"><div class="flex items-center justify-between gap-4"><div class="min-w-0 flex-1"><h4 class="text-foreground group-hover:text-primary mb-3 font-medium transition-colors duration-200"><a href=/posts/python-standrad-library-pathlib/ class=block>Python Standrad Library - pathlib</a></h4><div class="text-muted-foreground flex items-center gap-4 text-xs"><div class="flex items-center gap-1"><svg class="h-3 w-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5A2 2 0 003 7v12a2 2 0 002 2z"/></svg>