Revisit PEP-3113

[Stefan2 (Stefan Pochmann)]

@sirosen

more than one is necessary

I mourned the loss just last month:

@Stefan2

A common solution is to group by difference to index:

groupby(enumerate(xs), lambda ix: ix[1] - ix[0])

That was so much nicer in Python 2, where we could do this:

groupby(enumerate(xs), lambda (i, x): x - i)