Improve NameMapper error message when using #set with None value

Hi there,

Look at the following code snippet:


from Cheetah.Template import Template

t = Template.compile(source="""
#set $a = None
#if $a.b
Impossible
#end if
""")

print t()


When executing this script, an exception is thrown:


Traceback (most recent call last):
  File "test_cheetah_set.py", line 11, in <module>
    print t()
  File "/var/lib/python-support/python2.5/Cheetah/Template.py", line
996, in __str__
    return getattr(self, mainMethName)()
  File "DynamicallyCompiledCheetahTemplate.py", line 84, in respond
NameMapper.NotFound: cannot find 'b' while searching for 'a.b'


The error messsage is misleading for template writers.  Of course the
error is not that Cheetah cannot find 'b', but rather that 'a' is
None.  The following error message would be more useful:

AttributeError: 'NoneType' object has no attribute 'b'

Any idea how to fix this?  I guess it involves changing the
NameMapper, that may also imply some C coding.

Cheers,
-- 
Jean-Baptiste Quenot
http://jbq.caraldi.com/

------------------------------------------------------------------------------
The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your
production scanning environment may not be a perfect world - but thanks to
Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700
Series Scanner you'll get full speed at 300 dpi even with all image 
processing features enabled. http://p.sf.net/sfu/kodak-com