[Pyrex] Sparse vectors using dicts in Pyrex.

[Daniel Yarlett]

Hi,

I'm having trouble finding any information on this question, so I hope  
the solution isn't too obvious.

I have decided to use Python dictionaries to encode sparse vectors  
that I work with (initial exploration suggested this was faster than  
using the sparse vector implementation in scipy). If a vector has a  
non-zero value at a given index, the integer index is used as key to  
the appropriate value. E.g. if the 7th element of a vector is equal to  
3.2 then I would write something like:

vector = {}
vector[7] = 3.2

This works pretty well, except that I wish to expose the dictionary  
type using Pyrex so that I can hopefully improve the speed of my  
implementation. I was wondering if anyone could point me to a simple  
example in which a Pyrex function receives a dictionary and (a) gets  
the integer keys (indices) of this dictionary, and (b) does something  
simple like computes the sum of the vector (where each value is cast  
as a double, say). As I said, I haven't been able to find any  
documentation on this, and my knowledge of the C API for Python is too  
underdeveloped to allow me to figure this out on my own.

Also, does anyone have any thoughts on the potential speed benefits of  
using Pyrex in this instance as opposed to using Python's built-in  
dictionary methods?

Many thanks,

Dan.