suggestions, comments on an "is_subdict" test

Chris Rebert clp2 at
Fri Apr 22 16:38:38 CEST 2011

On Fri, Apr 22, 2011 at 6:55 AM, Vlastimil Brom
<vlastimil.brom at> wrote:
> Hi all,
> I'd like to ask for comments or advice on a simple code for testing a
> "subdict", i.e. check whether all items of a given dictionary are
> present in a reference dictionary.
> Sofar I have:
> def is_subdict(test_dct, base_dct):
>    """Test whether all the items of test_dct are present in base_dct."""
>    unique_obj = object()
>    for key, value in test_dct.items():
>        if not base_dct.get(key, unique_obj) == value:
>            return False
>    return True
> I'd like to ask for possibly more idiomatic solutions, or more obvious
> ways to do this. Did I maybe missed some builtin possibility?
> I am unsure whether the check  against an unique object() or the
> negated comparison are usual.?

I second MRAB's all() suggestion. The use of object() as a higher-rank
None is entirely normal; don't worry about it.

Also, the following occurs to me as another idiomatic, perhaps more
/conceptually/ elegant possibility, but it's /practically/ speaking
quite inefficient (unless perhaps some dict view tricks can be

def is_subdict(sub, larger):
    return set(sub.items()).issubset(set(larger.items()))


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