> For instance if I had the following

> <Test>
>     <foo name="Something" value="${SOMEVAR}"/>
>     <foo name="SomethingElse" value="${OTHERVAR}"/>
> </Test>

> I would like to retrieve SOMEVAR and OTHERVAR. I noticed they are replaced by something like this in the templte

> SOMEVAR = context.get('SOMEVAR', UNDEFINED)

> so it seems like there might be a way to hook into the parsing stage?

> On Sep 12, 2012, at 5:20 AM, slide wrote:

> > I am using Mako inside of an application to provide templated generation
> of XML files. I would like to retrieve the expression values from a given
> template to allow users to override the value before it is rendered.

> > For instance if I had the following

> > <Test>
> >     <foo name="Something" value="${SOMEVAR}"/>
> >     <foo name="SomethingElse" value="${OTHERVAR}"/>
> > </Test>

> > I would like to retrieve SOMEVAR and OTHERVAR. I noticed they are
> replaced by something like this in the templte

> > SOMEVAR = context.get('SOMEVAR', UNDEFINED)

> > so it seems like there might be a way to hook into the parsing stage?

> its a little odd to tell exactly who/when knows what in this scenario.  
> It seems like there is some concept of templates coming from somewhere with
> variables declared in them, and some other code needs to call upon these
> templates, and needs to "know" what variables will be called.

> That is, i need something to happen in response to a variable being
> present in a template.

> Usually, when I have to do this kind of thing it's with Python string
> templates, but same idea, I use an object with __getattr__ or __getitem__
> on it.

> That is, template:

> variable one: ${namespace.FOO}
> variable two: ${namespace.BAR}

> usage:

> class MyNamespace(object):
>     def __getattr__(self, key):
>         print "namespace attribute %s called" % key
>         return "HELLO!"

> template.render(namespace=MyNamespace())

> This is kind of an entirely different approach to what you're looking for,
> but is very simple and performant.

> Otherwise, you truly need to know the names before anything is rendered,
> yes you'd have to dig into Lexer, lex the template, get the parsetree back,
> walk through it and look for undeclared_identifiers() stuck on nodes.  
> Take a look at lexer.py and parsetree.py to see how that works, a quick lex
> looks like:

> from mako.lexer import Lexer
> parsetree = Lexer("some template").parse()

> def find_undeclared(node):
>     stack = [node]
>     while stack:
>         node = stack.pop(0)
>         stack.extend(node.get_children())
>         if hasattr(node, "undeclared_identifiers"):
>             for ident in node.undeclared_identifiers():
>                 yield ident

> On Wednesday, September 12, 2012 7:13:54 PM UTC-7, Michael Bayer wrote:

>> On Sep 12, 2012, at 5:20 AM, slide wrote:

>> > I am using Mako inside of an application to provide templated
>> generation of XML files. I would like to retrieve the expression values
>> from a given template to allow users to override the value before it is
>> rendered.

>> > For instance if I had the following

>> > <Test>
>> >     <foo name="Something" value="${SOMEVAR}"/>
>> >     <foo name="SomethingElse" value="${OTHERVAR}"/>
>> > </Test>

>> > I would like to retrieve SOMEVAR and OTHERVAR. I noticed they are
>> replaced by something like this in the templte

>> > SOMEVAR = context.get('SOMEVAR', UNDEFINED)

>> > so it seems like there might be a way to hook into the parsing stage?

>> its a little odd to tell exactly who/when knows what in this scenario.  
>> It seems like there is some concept of templates coming from somewhere with
>> variables declared in them, and some other code needs to call upon these
>> templates, and needs to "know" what variables will be called.

>> That is, i need something to happen in response to a variable being
>> present in a template.

>> Usually, when I have to do this kind of thing it's with Python string
>> templates, but same idea, I use an object with __getattr__ or __getitem__
>> on it.

>> That is, template:

>> variable one: ${namespace.FOO}
>> variable two: ${namespace.BAR}

>> usage:

>> class MyNamespace(object):
>>     def __getattr__(self, key):
>>         print "namespace attribute %s called" % key
>>         return "HELLO!"

>> template.render(namespace=MyNamespace())

>> This is kind of an entirely different approach to what you're looking
>> for, but is very simple and performant.

>> Otherwise, you truly need to know the names before anything is rendered,
>> yes you'd have to dig into Lexer, lex the template, get the parsetree back,
>> walk through it and look for undeclared_identifiers() stuck on nodes.  
>> Take a look at lexer.py and parsetree.py to see how that works, a quick lex
>> looks like:

>> from mako.lexer import Lexer
>> parsetree = Lexer("some template").parse()

>> def find_undeclared(node):
>>     stack = [node]
>>     while stack:
>>         node = stack.pop(0)
>>         stack.extend(node.get_children())
>>         if hasattr(node, "undeclared_identifiers"):
>>             for ident in node.undeclared_identifiers():
>>                 yield ident

> That doesn't sound too bad, I appreciate the pointers and will give it the
> old college try as they say.

> slide