[Pyrex] newbie list processing question

[Daniel Ashbrook]

Robert Bradshaw wrote:
>> def addOne(l):
>>    return [i+1 for i in l]
 >> ...
> 
> This last implementation of addOne should work as is in Cython, and will 
> be nearly optimal (assuming your CPU has reasonable branch prediction). 
> However, if you are manipulating word-sized integers, using C arrays 
> will give you a manyfold over python arithmetic.

So in the real code, I'm actually doing float math. And I'll be wanting 
to return my results in a list object. There will be many thousands of 
float results; what's the best way to deal with that? Use a C-specific 
data structure to store the results then turn it into a list somehow?

> Did you do
> 
> cdef int i
> for i from 0 <= i < len(L):
>     ...

Ah, I missed the "cdef int i" part of it.

> In Cython, if one writes
> 
> L[i]
> 
> where i is a cdef int, then it checks to see at runtime if L is a list 
> and accesses its elements via a macro. Otherwise one can use 
> PyList_SetItem and friends, but as you have noticed that is cumbersome 
> (as well ahs being hard to read).

Oh ho! That works very nicely; I'll include code to help others in the 
future:

   cdef int i
   for i from 0 <= i < len(l):
     l[i] = l[i] + 1


Thanks for the help!


dan