[Zope] Is Zope syntax inconsistent ?

[Tres Seaver]

Glyph Lefkowitz <glyph@twistedmatrix.com>
> 
> On Fri, 10 Mar 2000, Phil Harris wrote:
> 
> > As someone earlier today on the list said, "if it's in quotes it's python"
> > (or something similar).
> >
> > Basically Python rules apply when using any expressions in zope dtml-var
> > and other tags.
> 
> I still think it's an inconsistent syntax.  It should be possible (by
> overriding __coerce__, I think?  I haven't had time to look this up yet)
> to make the == operator do something different.  AUTHENTICATED_USER is
> often used as a string (at least what I've seen of it ...)

When in doubt, read the fine manual.  The _actual_ syntax you are using is::

  <dtml-var name="AUTHENTICATED_USER">

which can be abbreviated (and is, by almost every Zopista) as:

  <dtml-var AUTHENTICATED_USER>

The "name" form of the var tag is the "preferred" one, for the types of
applications DTML is really designed for: simple scripting of objects built
in Python.  It does several "automagic" things with the name:

  - If it is callable, calls it, passing the current object, the
    current namespace, and the REQUEST;  it then replaces the object
    with the result of the call.

  - If it has a string coercion (__str__) method, calls that and
    replaces the object with the result.

This behavior is the Right Thing (TM) for simple scripting;  but it _isn't_
Pythonic (the automagic stuff smells more Perlish, really).

The "in quotes" version is really::

  <dtml-var expr="AUTHENTICATED_USER">

but can also be spelt (and mostly is)::

  <dtml-var "AUTHENTICATED_USER">

The "expr" form of the var tag evaluates the Python expression (in this case,
to the object AUTHENTICATED_USER).  For fairly obvious security reasons, the
evaluation takes place inside a restricted namespace, without the usual
builtins;  the "safe" builtins are made available as members of the
"_" namespace.

> 
> Also, "if it's in quotes it's in python", why do I need to do _.str()?
> why does dir() not work?  It seems like some pretty horribly munged sort
> of python...
> 
> > > I would expect an object to behave consistently wherever it was used - so
> > > if it renders/returns/evaluates to 'zope' inside a dtml-var I would expect
> > > it equally to render/return/evaluate to 'zope' inside a dtml-if.
> 
> > > If it doesn't then surely we have an inconsistent syntax. How do we know
> > > how any object is going to behave inside a dtml tag ?

The simplest disambiguation possible is to cease using the shortcut forms, and
always spell what you really want:

  <dtml-var name="AUTHENTICATED_USER">  <!-- DWIM: give me text!!! -->

or

  <dtml-var expr="AUTHENTICATED_USER.getUserName()"> <!-- DWIS,NWYTIM -->

Hope this helps!

Tres.
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Tres Seaver         tseaver@palladion.com    713-523-6582
Palladion Software  http://www.palladion.com