Cheetah error rendering / better template debugging.

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Hi There,

I  wrote a quick article for my blog on this
(http://www.sourceweaver.com/posts/better-cheetah-error-renderer). It
then occurred to me I should post to the cheetah list. I originally
searched the archives in vain when hunting for a solution. I hope this
helps the next person looking to do something similar.

In my current job I work with a Django web application used to manage
configuration files. Users of the system can create data and templates
in the web app. The problem I encountered was displaying errors
'nicely'. What I wanted was template errors to be rendered showing
which line and what problem occurred. After a lot of digging and code
experimentation I found the solution I was looking for.

For example I have the following template:

    src = """
    0
    1  hello there $XYZ
    2
    3  $notpresent
    4
    5  $XYZ['notpresent']
    6
    7
    8  A KeyError for an unkown key 'fish': $abc['fish']
    9
    10
    11 ${ 0/0 } A more general error.
    12
    """.strip()

Cheetah is given this data dictionary:

    # Data dict:
    d = dict(XYZ=123, abc={})

My cheetaherrorrender.render_showing_errors(src, d) renders the
template as follows:

    0
    1  hello there 123
    2
    ERROR on line 3, Cheetah.NameMapper.NotFound(cannot find
'notpresent'): 3  $notpresent
    4
    ERROR on line 5, exceptions.TypeError(unsubscriptable object):  5
$XYZ['notpresent']
    6
    7
    ERROR on line 8, exceptions.KeyError('fish'):   8  A KeyError for
an unkown key 'fish': $abc['fish']
    9
    10
    ERROR on line 11, exceptions.ZeroDivisionError(integer division or
modulo by zero):     11 ${ 0/0 } A more general error.
    12

This very quickly lets you debug and rectify problems. I can't find an
alternative approach to my solution. I'd welcome suggestions on how I
can improve the render_showing_errors(). I've attached my python code
however you can also get it from my site here:
http://www.sourceweaver.com/public/scripts/cheetaherrorrender.py

All the best,

Oisin

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