[Python-3000] Change to class construction? (original) (raw)
Nick Coghlan ncoghlan at gmail.com
Sun Jul 8 07:10:16 CEST 2007
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Terry Reedy wrote:
"Nick Coghlan" <ncoghlan at gmail.com> wrote in message news:468FA01A.6040707 at gmail.com... | In py3k it expands to: | | def (outermost): | %0 = [] | for x in outermost: | for y in seq2: | %0.append(x*y) # Special opcode, not a normal call | return %0 | %n = (seq1)
Why not pass both seq1 and seq2 to the function so both become locals? The difference of treatment is quite surprising.
The inner iterable expressions can't be evaluated early, as they need to be re-evaluated for each pass around the outer loop (or loops). An example where the iterable expression for the inner loop refers to the iteration variable of the outer loop should make that clear:
.>>> [y for x in range(4) for y in range(x)] [0, 0, 1, 0, 1, 2]
The advantage of the Py3k approach is that it eliminates the current semantic differences between a list comprehension and list() with a generator expression argument, while keeping most of the performance benefits of the special syntax.
Cheers, Nick.
-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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