[Python-Dev] decorate-sort-undecorate

Peter Norvig pnorvig at google.com
Wed Oct 15 20:27:40 EDT 2003

Greg Ewing wrote:
>    [x >> key(x) for x in l] # ascending sort
>    [x << key(x) for x in l] # descending sort
>(Well, we got print >> f, so it was worth a try...)

I hope you're not serious about that.  

As it turns out, I have a proposed syntax for something I call an
"accumulation display", and with it I was able to implement and test a
SortBy in about a minute.  It uses the syntax

>>> [SortBy: abs(x) for x in (-2, -4, 3, 1)]
[1, -2, 3, -4]

where SortBy is an expression (in this case an identifier bound to a
class object), not a keyword.  Other examples of accumulation displays

    [Sum: x*x for x in numbers]
    [Product: Prob_spam(word) for word in email_msg]
    [Min: temp(hour) for hour in range(24)]
    [Top(10): humor(joke) for joke in jokes]
    [Argmax: votes[c] for c in candidates]

You can read the whole proposal at http:///www.norvig.com/pyacc.html

-Peter Norvig

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