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

[Shane Hathaway]

[Paul Winkler]
>>>I guess I don't understand the goal. Are we trying to make it
>>>so that zpt authors don't have to know any python?

[Chris Withers]
>>For me, that would be ideal...

[Paul Winkler]
>>>I really think that's a mistake.

Guys, that line of thinking is a distraction.  ZPT authors ought to 
learn Python.  The issue is deeper than that.  I'll explain below.

[Paul Winkler]
> Assuming that TALES python expressions are banned/discouraged/whatever, 
> [...]

Python expressions won't be banned.  I will never consider them 
discouraged for all cases, either.  There will always be a need for 
constructs like:

<div tal:condition="python: a == b">...</div>
<div tal:condition="python: (a and b) or c">...</div>

However, the following is quite bad:

<tal:x define="ss nocall:modules/Products/PythonScripts/standard">
  <a tal:attributes="href python: ss.url_quote(some_url)" />
</tal:x>

This is un-Pythonic in numerous ways.

- You can't use the import statement.  In fact, you can't use any 
statements at all--only expressions.

- The nocall: prefix.

- The name 'modules' is present automatically along with many other 
names that aren't in the Python builtins namespace.

- Importing using a path expression.

- Binding a variable to a value without an equal sign.

- You have to prefix Python expressions with "python:".

- You have to be careful not to use double quotes in expressions. 
(Ampersands and less-than/greater-than signs are tricky too.  Watch out 
for pairs of hyphens!)

Zope 2's method of slightly simplifying this is to write a two-line 
script and find it through implicit acquisition.  The overhead of 
invoking a script is somewhat large, but here's what the template would 
look like anyway.

<a tal:attributes="href python: here.url_quote(some_url)" />

Zope 3 will not have implicit acquisition.  In fact, no system but Zope 
2 has implicit acquisition.  That leaves us with no possible way to 
write the above statement in non-implicit Python!  No matter what you 
do, you need some help from another kind of expression.  Until recently, 
here was the way to write it in Zope 3.

<tal:x define="url_quote nocall:here/++acquire++url_quote">
   <a tal:attributes="href python: url_quote(some_url)" />
</tal:x>

That alternative is just as complicated and un-Pythonic as importing a 
module in a template.  I can't think of a better way to write this given 
the limitations of Zope 2 ZPT, without the giant implicit acquisition 
band-aid.  Can you?

Zope 3's new alternative looks about like this:

<a tal:attributes="href here/format:url_quote" />

To me, that's a vast improvment, and it's only one example.

You know what was actually wrong with DTML?  The lack of Python Scripts. 
  Without Python Scripts, everyone used DTML as a programming language. 
  Once Python Scripts came around, DTML became a reasonable templating 
language again.  If DTML used TALES expressions, it would be just as 
clean as ZPT.

Shane