Multidimensional Dictionaries: Possible?

[Tim Peters]

[Jerry Gardner]
> Are multidimensional dictionaries possible in Python?

Certainly.

> I'm sure they're possible, but I can't figure out the syntax.
>
> Here's how I do it in Perl:
>
> %dict = ();  # create empty dictionary
>
>
> $dict{$key1}{$key2} = $string;       # make an entry
> $newstring = ${dict{$key1}{$key2}};  # access an entry

Python doesn't have autovivification (unless you subclass UserDict to supply
it yourself).  You have to create intermediate data structures explicitly:

dict  = {}
dict[key1] = {}
dict[key1][key2] = string
newstring = dict[key1][key2]

Python rarely assumes you know what you're doing <wink -- but while that
sometimes adds more typing, it often saves your butt>.

Note too that you can use dict[key1, key2, ...] to "fake" a multidimensional
dict.  Sometimes that's more appropriate.  The equivalent in Perl
interpolates the multiple subscripts into a string; Python's dicts are more
general (can be indexed by any immutable object, not just strings), and
Python constructs a *tuple* of keys under the covers.  That's faster and
can't suffer accidental "superkey" collisions.