How to say $a=$b->{"A"} ||={} in Python?

[beginner]

On Aug 16, 9:32 pm, Carsten Haese <cars... at uniqsys.com> wrote:
> On Fri, 2007-08-17 at 00:53 +0000, beginner wrote:
> > $b is supposed to be a hash-table of hash-table. If a key exists in
> > $b, it points to another hash table. The $a=$b->{"A"} ||={} pattern is
> > useful when you want to add records to the double hash table.
>
> > For example, if you have a series of records in the format of (K1, K2,
> > V), and you want to add them to the double hash-table, you can do
> > $a=$b->{K1} || ={}
> > $a->{K2}=V
>
> What is the best solution in Perl need not be the best solution in
> Python. In Python you should just use a tuple as your dict key, i.e.
> a[k1,k2] = v, unless you have some other constraints you're not telling
> us.
>
> HTH,
>
> --
> Carsten Haesehttp://informixdb.sourceforge.net

I use tuples this way all the time. It is indeed very neat.  But it is
not a replacement for double hash-table.  If I want to retrieve
information just by K1, it is not efficient to index on (K1, K2).