Classes derived from dict and eval

[Kent Johnson]

Jeremy Sanders wrote:
> Hi -
> 
> I'm trying to subclass a dict which is used as the globals environment of
> an eval expression. For instance:
> 
> class Foo(dict):
>     def __init__(self):
>         self.update(globals())
>         self['val'] = 42
>                  
>     def __getitem__(self, item):
>         # this doesn't get called from the eval statement
>         print "*", item
>         return dict.__getitem__(self, item)
> 
> a = Foo()
> 
> print a['val']
> print eval('val*2+6', a)
> 
> The first print statements also prints "* val", but __getitem__ is never
> called by the evaluation in the eval statement.
> 
> Is this a bug? Does anyone have an idea for a workaround? I'm using
> Python 2.3.3.

Try Python 2.4.1:
Python 2.4.1 (#65, Mar 30 2005, 09:13:57) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> class Foo(dict):
 ...     def __init__(self):
 ...         self.update(globals())
 ...         self['val'] = 42
 ...     def __getitem__(self, item):
 ...         # this doesn't get called from the eval statement
 ...         print "*", item
 ...         return dict.__getitem__(self, item)
 ...
 >>> a = Foo()
 >>>
 >>> print a['val']
* val
42
 >>> print eval('val*2+6', a)
* val
90

Kent