[Zope-dev] Re: TALES idea: tuple unpacking

[Shane Hathaway]

Paul Winkler wrote:
> On Wed, Jul 23, 2003 at 02:04:51PM -0400, Fred L. Drake, Jr. wrote:
> 
>>There are those that consider using python: expressions in ZPT should
>>be discouraged, primarily because it's yet another syntax for a web
>>developer to learn.
>>
>>I'm not necessarily one of them, but I am sympathetic with that
>>reasoning.

That's not my reasoning either. :-)

My feeling is that you should avoid mixing syntaxes in a single 
document.  The more syntaxes you mix, the more perfection you require of 
developers.  Take the following code:

<pre tal:content="python: text.replace('\\n', '<br /')" />

This code has at least four errors (one XML, one HTML, one ZPT, one 
Python--can you spot them?), but it will work anyway without complaint. 
  This is hard to debug because it requires complete understanding and 
perfect spelling of four languages at once: XML, ZPT, HTML, and Python.

I wholeheartedly agree that newcomers should learn Python as well as 
ZPT, but there should be a clean separation of the two.

> My concern is that ZPT will grow so many conveniences that it will 
> become easier to abuse it in the same way that DTML has been 
> widely abused. New zope developers will then be more tempted to
> avoid python ("i don't have time to learn another language") and
> with the best intentions will do themselves a serious disservice: 
> a lot of things will still be unnecessarily difficult compared to 
> using python, and a lot of logic will be in templates where it 
> doesn't belong.

I have a slightly different concern.  You're concerned that people will 
use path expressions when they could use Python expressions.  I'm 
concerned that people will use *any* kind of complicated expressions 
instead of Python code blocks.  To me, the choice between path 
expression and Python expression isn't very meaningful; either way I'm 
putting logic in a template, and if it's too complicated, it doesn't 
belong there.  The better goal is to move complicated logic out of 
templates and into Python code blocks, don't you think?

I know of two ways to avoid writing complicated expressions in templates:

1. Move complicated expressions into Python code blocks.

2. Provide a simpler equivalent for complicated expressions.

Prefixes in the middle of path expressions attacks #2.

Shane