Asymmetry in globals __getitem__/__setitem__

[robert at robertlehmann.de]

On Friday, June 13, 2014 8:07:45 AM UTC+2, Marko Rauhamaa wrote:
> 
> The documentation is a bit vague about it:
> 
>    If only globals is provided, it must be a dictionary, which will be
>    used for both the global and the local variables. If globals and
>    locals are given, they are used for the global and local variables,
>    respectively. If provided, locals can be any mapping object.


Interesting.  This paragraph explicitly states "locals can be any mapping object," but that seems to be false:


class Namespace(dict):                                                          
    def __getitem__(self, key):                                                 
        print("getitem", key)                                                   
    def __setitem__(self, key, value):                                          
        print("setitem", key, value)                                            
                                                                                
def fun():                                                                      
    x  # should call locals.__getitem__                                         
    y = 1  # should call locals.__setitem__                                     
                                                                                
exec(fun.__code__, {}, Namespace())


Neither __getitem__ nor __setitem__ seem to be called on the local variables.