Re: PL/Python adding support for multi-dimensional arrays

On 10/01/2016 02:45 AM, Jim Nasby wrote:
> On 9/29/16 1:51 PM, Heikki Linnakangas wrote:
>> Now, back to multi-dimensional arrays. I can see that the Sequence
>> representation is problematic, with arrays, because if you have a python
>> list of lists, like [[1, 2]], it's not immediately clear if that's a
>> one-dimensional array of tuples, or two-dimensional array of integers.
>> Then again, we do have the type definitions available. So is it really
>> ambiguous?
>
> [[1,2]] is a list of lists...
> In [4]: b=[[1,2]]
>
> In [5]: type(b)
> Out[5]: list
>
> In [6]: type(b[0])
> Out[6]: list
>
> If you want a list of tuples...
> In [7]: c=[(1,2)]
>
> In [8]: type(c)
> Out[8]: list
>
> In [9]: type(c[0])
> Out[9]: tuple

Hmm, so we would start to treat lists and tuples differently? A Python 
list would be converted into an array, and a Python tuple would be 
converted into a composite type. That does make a lot of sense. The only 
problem is that it's not backwards-compatible. A PL/python function that 
returns an SQL array of rows, and does that by returning Python list of 
lists, it would start failing.

I think we should bite the bullet and do that anyway. As long as it's 
clearly documented, and the error message you get contains a clear hint 
on how to fix it, I don't think it would be too painful to adjust 
existing application.

We could continue to accept a Python list for a plain composite type, 
this would only affect arrays of composite types.

I don't use PL/python much myself, so I don't feel qualified to make the 
call, though. Any 3rd opinions?

- Heikki