Delete items in nested dictionary based on value.

[Dale Strickland-Clark]

Brian L. Troutwine wrote:

> I've got a problem that I can't seem to get my head around and hoped
> somebody might help me out a bit:
> 
> I've got a dictionary, A, that is arbitarily large and may contains
> ints, None and more dictionaries which themselves may contain ints,
> None and more dictionaries. Each of the sub-dictionaries is also
> arbitrarily large. When pretty printing A, in the context I'm using A
> for, it's rather helpful to remove all key:value pairs where value is
> None. So I'd like to be able to define a function dict_sweep to recurse
> through A and del all the keys with None as a value.
> 
> I feel like the solution is right on the tip of my tounge, so to speak,
> but I just can't quite get it. Anyway, here's the best I've come up
> with:

How about this:

def dict_sweep(dictionary):
        for k, v in dictionary.items():
                if v is None:
                        del dictionary[k]
                if type(v) == type({}):
                        dict_sweep(v)
                        #if len(v) == 0:
                        #       del dictionary[k]


A_in = {1: {2: 2, 3: {1: None, 2: 2}}, 2: 2, 3: None}

B_in = {1: {1: {1: None, 2: {1: None}}, 2: 2, 3: None}}

dict_sweep(A_in)
dict_sweep(B_in)
print A_in
print B_in

>>> {1: {2: 2, 3: {2: 2}}, 2: 2}
>>> {1: {2: 2}}


It doesn't produce the output you expect for B_in, but your brackets didn't
match and I'm not sure where the extra close should be. Also, I suspect
you're wanting to delete empty dictionaries but I don't see that mentioned
in the text. If that is so, include the two commented statements.
-- 
Dale Strickland-Clark
Riverhall Systems - www.riverhall.co.uk