On 2011-10-08 19:48, yoch melka wrote:

I would like to use backreferences in list comprehensions (or other comprehensions), such as :

[[elt for elt in lst if elt] for lst in matrix if \{1}] # \{1} is back-reference to filter result of the # first comprehension ([elt for elt in lst if elt])

It would be possible to do this ?

I don't think the syntax you propose is going to fly, but a similar feature has been discussed before on this list. I prefer this version:

[[elt for elt in lst if elt] as r for lst in matrix if r]

But I don't have much hope that it will ever get in.

FWIW, the example can already be written in several ways in current python, e.g.:

1) [r for lst in matrix for r in ([elt for elt in lst if elt],) if r] 2) filter(None, ([elt for elt in lst if elt] for lst in matrix))

HTH

- Jacob