Blocking A function blocks when it waits for something to happen before returning. A function may block for many reasons: network I/O, disk I/O, mutexes, etc. In fact, every function blocks, at least a with Python control sequences and expressions embedded within the markup: <title>{{ title }}title>

{% for item in items %}
• {{ escape(item) }}
{% end %} RequestHandler): def get(self): items = ["Item 1", "Item 2", "Item 3"] self.render("template.html", title="My title", items=items) Tornado templates support control statements and expressions. Control statements

Blocking A function blocks when it waits for something to happen before returning. A function may block for many reasons: network I/O, disk I/O, mutexes, etc. In fact, every function blocks, at least a control sequences and expressions embedded within the markup: <title>{{ title }}title>

{% for item in items %}
• {{ escape(item) get(self): items = ["Item 1", "Item 2", "Item 3"] self.render("template.html", title="My title", items=items) Tornado templates support control statements and expressions. Control statements

工具来抓取两个网页，拉取各自的 <title> 元素，并打印出第一个完成全部过程的那个页面的 标题。 定义 page_title 函数 让我们开始编写一个函数，它获取一个网页 URL 作为参数，请求该 URL 并返回标题元素的文 本（见示例 17-1）。 文件名：src/main.rs use trpl::Html; async fn page_title(url: &str) -> Option Html::parse(&response_text) .select_first("title") .map(|title_element| title_element.inner_html()) } 首先，我们定义一个名为 page_title 的函数，并使用了 async 关键字标记。接着我们使用 trpl::get 函数来获取传入的任意 URL，然后使用 HTML 作为更丰富数据结构来操作的数 据类型。特别是我们可以使用 select_first 方法来找出给定 CSS 选择器（selector）中第一 个匹配元素。通过传递字符串 "title"，我们会得到文档中的第一个 <title> 元素，如果它存 在的话。由于可能没有任何匹配的元素，select_first 返回一个 Option。最后 我们使用 Option::map 方法，它允许我们在

Evaluation Scope of Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . 83 8.16 Do-Block Syntax for Function Arguments . . . . . . . . . . . . . . . . . . . . . . . . 83 8.17 Function composition encounter! help?> begin search: begin disable_sigint reenable_sigint begin begin...end denotes a block of code. If you already know Julia a bit, you might want to peek ahead at Performance Tips and Workflow the rounding can be changed only within the execution of a particular block of code by using the same functions with a do block: julia> setrounding(BigFloat, RoundUp) do BigFloat(1) + parse(BigFloat

Evaluation Scope of Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . 83 8.16 Do-Block Syntax for Function Arguments . . . . . . . . . . . . . . . . . . . . . . . . 83 8.17 Function composition encounter! help?> begin search: begin disable_sigint reenable_sigint begin begin...end denotes a block of code. If you already know Julia a bit, you might want to peek ahead at Performance Tips and Workflow the rounding can be changed only within the execution of a particular block of code by using the same functions with a do block: julia> setrounding(BigFloat, RoundUp) do BigFloat(1) + parse(BigFloat

Evaluation Scope of Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . 88 9.16 Do-Block Syntax for Function Arguments . . . . . . . . . . . . . . . . . . . . . . . . 88 9.17 Function composition encounter! help?> begin search: begin disable_sigint reenable_sigint begin begin...end denotes a block of code. If you already know Julia a bit, you might want to peek ahead at Performance Tips and Workflow the rounding can be changed only within the execution of a particular block of code by using the same functions with a do block: julia> setrounding(BigFloat, RoundUp) do BigFloat(1) + parse(BigFloat

Evaluation Scope of Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . 88 9.16 Do-Block Syntax for Function Arguments . . . . . . . . . . . . . . . . . . . . . . . . 88 9.17 Function composition encounter! help?> begin search: begin disable_sigint reenable_sigint begin begin...end denotes a block of code. If you already know Julia a bit, you might want to peek ahead at Performance Tips and Workflow the rounding can be changed only within the execution of a particular block of code by using the same functions with a do block:CHAPTER 5. INTEGERS AND FLOATING-POINT NUMBERS 27 julia> setrounding(BigFloat

Evaluation Scope of Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . 88 9.16 Do-Block Syntax for Function Arguments . . . . . . . . . . . . . . . . . . . . . . . . 88 9.17 Function composition encounter! help?> begin search: begin disable_sigint reenable_sigint begin begin...end denotes a block of code. If you already know Julia a bit, you might want to peek ahead at Performance Tips and Workflow the rounding can be changed only within the execution of a particular block of code by using the same functions with a do block:CHAPTER 5. INTEGERS AND FLOATING-POINT NUMBERS 27 julia> setrounding(BigFloat

Evaluation Scope of Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . 88 9.16 Do-Block Syntax for Function Arguments . . . . . . . . . . . . . . . . . . . . . . . . 88 9.17 Function composition encounter! help?> begin search: begin disable_sigint reenable_sigint begin begin...end denotes a block of code. If you already know Julia a bit, you might want to peek ahead at Performance Tips and Workflow the rounding can be changed only within the execution of a particular block of code by using the same functions with a do block:CHAPTER 5. INTEGERS AND FLOATING-POINT NUMBERS 27 julia> setrounding(BigFloat

Evaluation Scope of Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . 88 9.16 Do-Block Syntax for Function Arguments . . . . . . . . . . . . . . . . . . . . . . . . 88 9.17 Function composition encounter! help?> begin search: begin disable_sigint reenable_sigint begin begin...end denotes a block of code. If you already know Julia a bit, you might want to peek ahead at Performance Tips and Workflow the rounding can be changed only within the execution of a particular block of code by using the same functions with a do block:CHAPTER 5. INTEGERS AND FLOATING-POINT NUMBERS 27 julia> setrounding(BigFloat