How to access elemenst in a list of lists?

[Terry Reedy]

On 5/10/2011 3:22 AM, Algis Kabaila wrote:
> On Tuesday 10 May 2011 11:25:59 Terry Reedy wrote:

>  > class listwrap:
>  >  def __init__(self, lis):
>  >   self._list = lis
>  >  def __getitem__(self, dex):
>  >   i,j = dex
>  >   return self._list[i][j]
>
>  > # __setitem__: exercise for reader

>  > l = listwrap([[1,2,3],['a','b','c']])
>  > print(l[0,2],l[1,0])
>  > # 3 a

> Thank you for your response. I have to confess that I do have the cludge
> of an answer to my own quesion, but it is a cludge; Your method looks
> much better, though I don't think it is complete - this subclassing of
> __getitem__ appears to stop simple list access, i.e. if li = [1, 2 ,3],
> it seems to me that print(li[2]) would raise an exception, no?

Yes, there really should be a guard condition: if isinstance(x tuple)
or try: len(x) == 2. A __getattr__ method could be added to forwar other 
list methods to the wrapped list. One could try subclassing instead of 
wrapping, but some special methods have a fast path access for builtins 
that bypasses subclass methods. I think __getitem__ may be one such. 
Wrapping is safe in that respect.

-- 
Terry Jan Reedy