ZPT教程之二:熟练使用TAL/TALES

原作者 : ThankCreate
原文链接: http://www.thankcreate.com/tech/220
转贴请注明出处,支持原创,感激不尽。


1. TAL与TALES总述

在前续教程中我已经提到,ZPT的三大核心是TAL,TALES和METAL。而前两者在实际应用中往往是一起使用的。在此就合并作一个教程来讲了。
TAL语句一般以tal为前缀。目前笔者使用的ZPT版本中,TAL标准为1.4。其实其语法一共也就以下几种:
define,attribute,condition,content,replace,repeat,on-error,omit-tag
TALES用起来则相对更灵活,它实际上就是定义了一套表达式的表示方法。
在后面的教程中,我们将以TAL为纲,再灵活穿插TALES的相关知识。

2. TAL分类详解

1.1 define

Define语句的主要作用是定义变量并赋值

语法:
argument::= attribute_statement [‘;’ attribute_statement]*
attribute_statement::= attribute_name expression
attribute_name ::= [namespace ‘:’] Name
namespace ::= [local | global]
通俗一点即tal:define=“[local | global] 变量名 TALES表达式 [;重复参数] “
如果你想在表达式中用分号,需要用两个连续的分号表示

先看个例子:

I am a Student of <span tal:define="school string:HUST"
tal:content="string:$school">school here</span>

输出为:
I am a Student of HUST

注意,此处的变量名为school, 而值是一个字符串型,所以我们要在”HUST”前面加上一个string前缀。而要引用这个变量的话,理论上来说我们得写成string:$school的形式,但是实验发现其实不写也可以。
变量不光可以定义成string类型,借助于python的扩展表达式,我们还可以将其定义成这样

25 * 10 =  <span tal:define="result  python: 25 * 10"
tal:content="result">result here</span>

输出为
25 * 10 = 250

细心的读者可能发现了,以上的例子并没有用到global或是local这样的命名空间修饰。这是因为缺省情况下,其默认值为local,即当前定义的变量只能在当前的标签及其子标签中有意义。
在下面的例子中,我们将看到由于定义的命名空间不同带来的效果区别。

<span tal:define="global fruit string:banana"></span>
<span tal:define="fruit string:apple"  tal:content="fruit">value</span><br>
<span tal:content="fruit"></span>

输出为

Apple
banana

1.2 content与 replace

在教程一中我已经提到过,content与replace的唯一区别就是replace会把自身的元素标签也替换掉。例如:

<i tal:define="fruit string:apple"  tal:content="fruit"></i><br>
<i tal:define="fruit string:apple"  tal:replace="fruit"></i>

输出即为:

<i>apple</i><br>
apple

1.3 attributes

attribute方法会替代原有元素标签中的属性

语法:
argument::=attribute_statement[‘;’ attribute_statement]*
attribute_statement::= attribute_name expression
attribute_name ::= [namespace ‘:’]
Name namespace ::= Name
即tal:attributes=”要替代的属性名? TALES表达式[;重复参数]”

<a tal:attributes="href string:http://www.thankcreate.com">Hello</a><br>
<span><font tal:attributes="size string:10">Am I big?</font></span>

1.4 condition

condition的作用类似于if。当其后所接表达式为假时,将把所在的标签及其子标签一并删除
语法为tal:condition=“TALES表达式”
此处的TALES表达式会经常与python前缀连用,比如说,如果我们希望当用户名为admin时,显示”Welcome to configuration page”,则有如下的写法:

<span tal:define="global name string:admin"></span>
<span tal:condition="python:name=='admin'">
Welcome to the configuration page
</span>

这里用到了==运算符表示是否相等。相应的,以下运算符都可以作为python语句嵌入
!=
<= >=
< >
and not or.
如 python:name == ‘admin’ and password==’hello’

1.5 omit-tag

omit-tag与condition有些相似,不同之处是此方法删除的仅仅是标签,而不是像condition一样把标签与内容一并删掉。

<i tal:omit-tag="python:'1' == '1'" >Haha</i>

那么输出为是
Haha
而不是
Haha

另外需要注意的一个地方是,omit-tag是为”真”时删除,而condition是为”假”时删除。

1.6 repeat

repeat算是tal各种方法里较复杂的一种了。

其语法为:
argument ::= variable_name
expression variable_name ::= Name
记性好的朋友可能记得我在教程一里已经给出一个 repeat的例子了,我们现在还是以它来说事吧:

<tr tal:repeat=”book python:’Thinking in C++’, ‘Yearbook of Dian 2010 ’, ‘Effective  C ++’ ”>
     <td tal:content = “book”>The text here is not important</td>
</tr>

repeat所在的那个标签及其子标签一直重复输出,而变量book实际上是一个迭代器。
所以最后就会生成一个三行一列的表格了。
但是在接下来的例子中我们会看到,repeat的用法不限于此。

<ul tal:define="global array_source python:'a','b','c','d'">
<li tal:repeat="array array_source">
<span tal:condition="repeat/array/start">Here is the start:</span>
<span tal:condition="repeat/array/end">Here is the end:</span>
<span tal:content="array"></span>
<span tal:condition="repeat/array/end"><br>
  Size of the array: <span tal:replace="repeat/array/length "></span>
</span>
</li>
</ul>

输出为:
Here is the start: a
b
c
Here is the end: d
Size of the array: 4
此例的重点是“repeat/array/”这一TALES表达式。”repeat”这个变量本身也是TALES的内建变量之一。其中repeat/array/start将会判断当前是否是队列的第一个,end同理。/length会得到数组的长度。官方文档给出了repeat量的所有属性:

index repetition number, starting from zero.
number repetition number, starting from one.
even true for even-indexed repetitions (0, 2, 4, …).
odd true for odd-indexed repetitions (1, 3, 5, …).
start true for the starting repetition (index 0).
end true for the ending, or final, repetition.
length length of the sequence, which will be the total number of repetitions.
letter count reps with lower-case letters: “a” – “z”, “aa” – “az”, “ba” – “bz”, …, “za” – “zz”, “aaa” – “aaz”, and so forth.
Letter upper-case version of letter.

1.7 on-error

on-error方法会设定当所在标签在出错时输出的内容。
考虑这样一个场景,模板页FormAction将接收一个来自method=”POST”的Form传过来的值,包括一个name值和一个password(虽然password是绝不可能用GET传值的,但是估且这么设定吧)。
新建一个ID名为Form的Page Template,修改页面至如下
Form版本1:

<form action="FormAction" method="POST">
admin name:<input type="text" name="name">
password:<input type="text" name="password">
<input type="submit">
</form>

在同一个文件夹下新建ID名为FormAction的Page Template,修改页面至如下

FormAction版本1:

name:<span tal:content="request/form/name"></span><br>
password:<span tal:content="request/form/password"></span>

正常情况下,Form中输入什么,在FormAction页中就会显示什么。
但是如果由于某些原因导致原Form中的password输入框被删除掉了呢?
如把原Form改为如下形式:
Form版本2:

<form action="FormAction" method="POST">
admin name:<input type="text" name="name">
<span tal:condition="python:1 == 2">password: <input type="text" name="password"></span>
<input type="submit">
</form>

那么当执行submit后,FormAction就会因为找不到request/form/password量而报错,导致整个页面都崩溃。这个时候on-error就可以派上用场了。

修改原FormAction至如下:
FormAction版本2

name:<span tal:on-error="string:Name value not found"
 tal:content="request/form/name"></span><br>
password:<span tal:on-error="string:Password value not found"
 tal:content="request/form/password"></span>

那么再次执行提交后,输出的则是如下的页面了:

name:thankcreate
password:Password value not found

到此为止,TAL的基本用法就介绍完了,想得到更全面的资料请至

http://wiki.zope.org/ZPT/TALSpecification14

3. TALES用法总结

在以上TAL的讲解部分中相信大家对于TALES的用法已经有了一些认识了,现在就来作个系统性的学习吧。
TALES表达式主要分以下几种

path locate a value by its path.
exists test whether a path is valid.
nocall locate an object by its path.
not negate an expression
string format a string
python execute a Python expression

大部分大家已经在之前的教程中或多或少的用过了,可能比较陌生的是exits和nocall。

exits作用是是检查一个路径是否是有效
比如

<p tal:condition="not:exists:request/form/number">
  Error: number not exists
</p>

这个例子会检测request/form/number是否有效,如果无效,则会输出”Error: number not exists”。

nocall的用法描述与path有些类似,所不同的是它所定义的量是一个对象,而不是值。多说无益,还是举例子。之前大家见过request/form/name的用法,但是如果我们想嫌它太长,想把request/form定义为一个变量,则必须写成tal:define=”myform nocall:request/form”。

关于TALES的更多信息,详见http://docs.zope.org/zope2/zope2book/AppendixC.html.

7 thoughts on “ZPT教程之二:熟练使用TAL/TALES

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