suggestions, comments on an "is_subdict" test

Peter Otten __peter__ at
Fri Apr 22 16:38:18 CEST 2011

Vlastimil Brom 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.?
> (The builtin exceptions are ok, in case anything not dict-like is
> passed. A cornercase like >>> is_subdict({}, 4)
>>>> True
> doesen't seem to be worth a special check just now.)

I would avoid the unique object because it's neither hard nor costly:

def is_subdict(test, base):
    return all(k in base and base[k] == v for k, v in test.iteritems())

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