[ZPT] sequence unpacking syntax in TAL

[Charlie Clark]

On 2003-07-14 at 00:14:45 [+0200], Dieter Maurer wrote:
>  > By analogy with this, we could also provide limited dict "unpacking" 
>  > for keys that are valid variable names (common case in my experience), 
>  > like tal:define="{key1 key2} mapvar".
> 
> Didn't we want to keep TAL as simple as possible?
> Wasn't out motto: simple (and explicite) is beautyful.

While I can understand tuple unpacking in TAL working just as in Python I 
must agree with Dieter that TAL should be kept as simple as possible. It's 
become second nature to me to write PythonScripts to work with TAL.

Looking at the supplied examples:

  <div tal:define=
       "userid, host  python:context.email_address.split('@', 1)"
       >

This seems highly contrived and unrepresentative and not the kind of TAL I 
would like to leave for anyone to have to figure out.

By extension, this should be useful with tal:repeat loops as well:

  <tr tal:repeat=
       "userid, name, email, favcolor  context/user_info"
       >
    <td tal:content="userid"> user id </td>
    <td><a href="mailto:address"
           tal:attributes="href string:mailto:$email"
           tal:content="name"> user name </a></td>
    <td>Favorite color:
        <span tal:replace="favcolor"> color name </span> </td>
  </tr>

While this makes more sense I had to do a double-take as to why it is 
tal:repeat and not tal:define. I think I would have problems with this and 
I don't see any significant advantage over
<tr tal:repeat results context/user_info>
<td tal:content="results/userid">
</tr>

The namespace remains clear because it is explicit and all we have is some 
additional typing.

If <tal:define="a, b, c, d 1, 2, 3, 4"> is to be allowed then I do not 
agree with Evan's suggestion for new syntax for what would be a special 
case but 
<tal:define="(a, b, c, d) (1, 2, 3, 4)"> should be allowed for legibility. 
Unpacking errors due should be presented as such with no catchalls: you 
have to know what you're doing with tuple-unpacking and there is no need to 
duplicate Python functionality.

Just my thoughts.

Charlie