Idea for pure-python templates using AST.

anand jeyahar anand.ibmgsi at gmail.com
Tue Aug 16 18:16:07 CEST 2011


Hi all,
   I did it. Finally managed to port mysqltuner.pl to python. Was a
real pain in the butt doing it from bottom up manually, without ever
really learing perl syntax. But i finally got it done. Now i need help
testing it. find it here.
 git at github.com:anandjeyahar/mysqlDbAdmin-python.git.

Also i never really thought about design. Just blindly/mechanically,
translated from perl to python. So criticize and let me know how i can
improve this.

Thanks and Regards,
==============================================
Anand Jeyahar
https://sites.google.com/site/anandjeyahar
==============================================
The man who is really serious,
with the urge to find out what truth is,
has no style at all. He lives only in what is.
                  ~Bruce Lee

Love is a trade with lousy accounting policies.
                 ~Aang Jie




On Tue, Aug 16, 2011 at 18:02, aspineux <aspineux at gmail.com> wrote:
> On Aug 16, 1:33 pm, "Paul Wray" <paul.w... at det.nsw.edu.au> wrote:
>> Hello all
>>
>> Ive had what I think is a great idea for pure-python templates (I can almost
>> hear the groans, bear with me...)
>>
>> For the impatient, proof of concept is athttp://pastie.org/2379978
>> demonstrating simple substitution, balanced tags using context manager,
>> subtemplates,  and template inheritance.
>
> You code fail, see below for other comment
>
> Traceback (most recent call last):
>  File "Download/pastie-2379978.rb", line 108, in <module>
>    make_template(template1)
>  File "Download/pastie-2379978.rb", line 60, in make_template
>    ast.fix_missing_locations(astFromSrc)
>  File "/usr/lib/python2.6/ast.py", line 133, in fix_missing_locations
>    _fix(node, 1, 0)
>  File "/usr/lib/python2.6/ast.py", line 132, in _fix
>    _fix(child, lineno, col_offset)
>  File "/usr/lib/python2.6/ast.py", line 132, in _fix
>    _fix(child, lineno, col_offset)
>  File "/usr/lib/python2.6/ast.py", line 121, in _fix
>    if 'lineno' in node._attributes:
> AttributeError: 'arguments' object has no attribute '_attributes'
>
>
>
>
>>
>> I'm posting here to get opinions on:
>> * the merits of the idea, (or otherwise!)
>> * whether there are any established/mature templating systems that use this
>> approach, or whether its come up before,
>> * ideas for improvements and advice on other aspects such as sandboxing
>> * of course, to share the idea in case others want to use it
>
> This is very original ! First time I see it. I like it.
> But how to debug large template ?
> How to find/detect a missing </TAG> ?
> This is very important. This is one big advantage of Genshi over Kid
> How to report the correct error at the correct line ?
> How to find/get nice editor to edit large template ?
>
>
>>
>> Background: Ive been working on an application that recursively renders
>> html/xml documents from heterogenoeus trees, with separate classes for each
>> document component. First I built my own renderer but was dissatisfied with
>> the repetitive code. Then looked at Mako and Jinja, and used Jinja but was
>> still disatisfied, because I still needed a render method in each class to
>> do preparation, and also the template which was centrally managed by the
>> Jinja loader and environment. I found a way to call templates recursively
>> via Jinja filters, but was not sure that it wouldnt blow up in my face, so I
>> also had separate calls to render the children of each node, and then feed
>> the value to the parent template. I kept thinking that there must be a way
>> to get the brevity and clarity of declarative templates, plus the simplicity
>> of pure python loops, tests and function calls.
>>
>> The idea:
>> Python syntax allows a statement to be a bare literal or identifier. These
>> have no effect on the program.
>>
>> So the function below is legal python:
>>
>> def myFunc():
>>     'a'
>>     x = 45
>>     'b'; 'c'; x
>>
>> So is this (within the appropriate class context of course):
>>
>> def body(self, r):
>>         '<h1>'; self.heading; '</h1>'
>>         '<ul>'
>>         for itm in self.items:
>>             '<li>'; itm; '</li>'
>>         '</ul>'
>>
>> The idea is simply to use python ASTs to transform this code so that it
>> accumulates the values of the bare expressions.
>
> You could call it PHP :-)
>
>>
>> I think this give the best of both worlds - declarative syntax for the
>> template literals, but in a pure python context, giving you all the power of
>> python control statements, classes etc.
>>
>> For application contexts outside pure python code (ie user-created
>> templates) , it would be simple to extend the technique to creating template
>> functions from strings, and insert the resulting methods into a namespace
>> for execution.)
>>
>> I think, given the technique is already working with the AST, that
>> sandboxing should not be too hard either - advice on this aspect would be
>> appreciated.
>
>
> Maybe a good idea.
> But still a lot of work to get the level of existing libraries.
>
> Maybe better if mixed with other tools like Genshi to create widget.
> Maybe next toscawidget could use such a technique.
>
>
> Thanks for sharing
>
>>
>> Paul Wray
>
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