Python Disk-Based Dictionary

Question

I was running some dynamic programming code (trying to brute-force disprove the Collatz conjecture =P) and I was using a dict to store the lengths of the chains I had alread

Answer 1

The shelve module may do it; at any rate, it should be simple to test. Instead of:

self.lengths = {}

do:

import shelve
self.lengths = shelve.open('lengths.shelf')

The only catch is that keys to shelves must be strings, so you'll have to replace

self.lengths[indx]

with

self.lengths[str(indx)]

(I'm assuming your keys are just integers, as per your comment to Charles Duffy's post)

There's no built-in caching in memory, but your operating system may do that for you anyway.

[actually, that's not quite true: you can pass the argument 'writeback=True' on creation. The intent of this is to make sure storing lists and other mutable things in the shelf works correctly. But a side-effect is that the whole dictionary is cached in memory. Since this caused problems for you, it's probably not a good idea :-) ]

Answer 2

With a little bit of thought it seems like you could get the shelve module to do what you want.