[albatross-users] Our first custom tag

[Michael C. Neel]

Have you considered using a lookup?  You could have a lookup:

<al-lookup name="classtag">
	<al-item expr="0"> </al-item>
	<al-item expr="1">class="alt1"</al-item>
	<al-item expr="2">class="alt2"</al-item>
	<al-item expr="3">class="alt3"</al-item>
</al-lookup>

...placed in a global template, then use:

<tr <al-value expr="i.value()" lookup="classtag"> >

..in the page.

Mike

> -----Original Message-----
> From: Gregory Bond [mailto:gnb at itga.com.au] 
> Sent: Sunday, November 10, 2002 7:12 PM
> To: albatross-users at object-craft.com.au
> Subject: [albatross-users] Our first custom tag
> 
> 
> We have an informal in-house style that says alternating rows 
> of table data 
> should have different background colors, so that it is easy 
> to keep track of 
> which row is which.  This is done by alternating the "class" 
> attribute of each 
> "<tr>" tag.  (Most of our existing intranet is built with 
> HTMLgen, which is 
> kind-of "inside-out" compared to Albatross, in that it is a 
> program to 
> generate HTML, rather than an HTML file containing 
> program-like elements.  
> Things like alternating class attributes is easy to do in 
> this style of 
> system.)
> 
> In trying to use Albatross, I wound up doing lots of code like
> 	<al-if expr="i.index() % 2">
> 		<tr>
> 	<al-else>
> 		<tr class="alt">
> 	</al-if>
> 
> Not only is this ugly to look at and a lot to type, it really 
> messes with the
> head of the HTML editor (I use xemacs) and buggers the indentation.
> 
> So we wrote an extension tag <alx-tr> to hide all this 
> nastyness.  I include 
> it here in case anyone else finds it interesting.
> 
> [To the Albatross team: Feel free to make this part of the official
> distribution.  This might also make a good case study in 
> custom tags for the
> manual!]
> 
> 
> 
> #! /usr/local/bin/python
> '''
> A collection of useful custom tag classes for use with the 
> albatross library.
> 
> To make these available, simply pass the class object to the
> register_tagclasses() member of the application object.
> 
> E.g.:
> 
> 	import itgatags
> 
> 	....
> 	class MyApp(SimpleApp):
> 	    def __init__(self):
> 		SimpleApp.__init__(self,......)
> 		for page_class in (.......):
> 		    self .register_page(page_class.name, page_class())
> 		for tag_class in (itgatags.TR,):
> 		    self .register_tagclasses(tag_class)
> 
> 
> 
> '''
> 
> from albatross.tags import ExprAttrMixin
> from albatross import EnclosingTag
> 
> class TR(EnclosingTag, ExprAttrMixin):
>     '''
>     <alx-tr expr="..." classes="alt1,alt2,alt3"> ... </alx-tr>
> 
>     Similar to <tr>, except that it evaluates expr (which must be an
>     integer) and then chooses a "class=" attribute for the <tr> tag
>     from those listed in the "classes" arg by taking "<expr> % <# of
>     classes>".  <expr> is often "i.index()" where i is an iterator
>     created by <al-for>.
> 
>     This is useful for having rows of the table with alternating or
>     successive styles.  Elements of the "classes" list may be empty
>     (i.e. "alt1,") or the empty string ("alt1,'',alt2") which will
>     produce a <tr> without a "class=" attribute.
> 
>     "classes" may be omitted and defaults to ",alt" (i.e. alternating
>     normal and "class=alt" styles.  Naturally, you will need some sort
>     of stylesheet definitions for these classes.
> 
>     Example:
>     <table>
>      <al-for iter="i" expr="...">
>       <alx-tr expr="i.index()" classes=",alt1,,alt2">
>        <td><al-value expr="i.value().name">.......</td>
>       </alx-tr>
>      </al-for>
>     </table>
>     This will produce a table where the odd rows are normal, but the
>     2nd and 4th rows have special class (and hence presumably special
>     formatting).
>     
>     <alx-tr counter="name" classes="'',alt1,alt2"> ... </alx-tr>
> 
>     Similar to the above, but instead of evaluating an expression,
>     this uses a counter with the given name in the ctx.locals space
>     (creating it with the value 0 if necessary).  The counter will be
>     incremented after it is used.  This is useful if a single table
>     contains rows from multiple <al-for> tags, or summary lines at the
>     bottom, or similar.  It can also count the number of rows for you!
> 
>     Example:
>     <table>
>      <al-for iter="i" expr="...">
>       <alx-tr name="row">
>        <td><al-value expr="i.value().name">.......</td>
>       </alx-tr>
>      </al-for>
>      <alx-tr name="row">
>       <td>TOTAL:........</dt>
>      <alx-tr>
>     </table>
>     <al-value expr="row"> Rows Added.
>     
>     Using a counter rather than the iterator.index() method ensures
>     that the TOTAL row has the appropriate and consistant class
>     attribute.
>     
>     '''
>     name = 'alx-tr'
> 
>     def __init__(self, ctx, filename, line_num, attribs):
>         EnclosingTag.__init__(self, ctx, filename, line_num, attribs)
>         if self.has_attrib('expr'):
>             self.compile_expr()
> 	    self.counter = ''
> 	elif self.has_attrib('counter'):
> 	    self.counter = self.get_attrib('counter')
> 	else:
>             self.raise_error('missing "counter" or "expr" attribute')
> 	if self.has_attrib('classes'):
> 	    cs = self.get_attrib('classes')
> 	    self.classes = []
> 	    for c in cs.split(','):
> 		if c == "''" or c == '""':
> 		    c = ''
> 		self.classes.append(c)
> 	else:
> 	    self.classes = ['', 'alt']
> 	    
>     def to_html(self, ctx):
> 	if self.counter:
> 	    if ctx.has_value(self.counter):
> 		val = ctx.get_value(self.counter)
> 	    else:
> 		val = 0
> 	else:				# expr
> 	    val = int(ctx.eval_expr(self.expr))
> 
> 	cls = self.classes[val % len(self.classes)]
> 	if cls:
> 	    ctx.write_content('<tr class="%s">' % cls)
> 	else:
> 	    ctx.write_content('<tr>')
> 
> 	self.content.to_html(ctx)
> 	ctx.write_content('</tr>\n')
> 
> 	if self.counter:
> 	    ctx.set_value(self.counter, val + 1)
> 
> 
> 
> 
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