Fast list traversal

[dineshv]

I want to see if there is an alternative method for fast list
traversal.  The code is very simple:

dict_long_lists = defaultdict(list)
for long_list in dict_long_lists.itervalues()
        for element in long_list:
                array_a[element] = m + n + p                # m,n,p
are variable numbers

The long_list's are read from a defaultdict(list) dictionary and so
don't need initializing.  The elements of long_list are integers and
ordered (sorted before placing in dictionary).  There are > 20,000
long_list's each with a variable number of elements (>5,000).  The
elements of long_list are immutable (ie. don't change).  The above
code is within a def function.

I've tried set() using defaultdict(set) but the elements are not
ordered.

What is the fastest way to traverse these long_list's sequentially
from the beginning to the end?  Maybe there is another data structure
that can be used instead of a list.

Dinesh