Qn: Nested dictionary cleanup

Peter Otten __peter__ at web.de
Mon Nov 3 23:02:19 CET 2003

Colin Brown wrote:

> My code fragment below:
> for key1 in dict1.keys():
>     for key2 in dict1[key1]:
>         if dict1[key1][key2] == None:
>             del dict1[key1][key2]
> gives the following error:
> RuntimeError: dictionary changed size during iteration
> Any suggestion on how to code this please.
> Thanks
> Colin Brown
> PyNZ

In addition to Emile van Sebille's fix, the following tries to avoid
dictionary lookups:

# dict1 is not changed so we need not copy the values
for innerdict in dict1.itervalues():
    # innerdict is changed so let's make a copy of the items
    for key, value in innerdict.items():
        if value is None:
            del innerdict[key]


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