On 30/04/2015 18:20, Ben Finney wrote:
Jon Ribbens <jon+use...@unequivocal.co.uk> writes:
If you use xrange() instead of range() then you will get an iterator
which will return each of the numbers in turn without any need to
create an enormous list of all of them.
If you use Python 3 instead of the obsolescent Python 2, the ‘range’
callable has this sensible behaviour by default.
When I first looked at Python 20 or so years ago this seemed to be the
standard way of writing a for-loop:
for i in range(N):
....
I remember being completely astonished at the time that 'range' actually
created a list of values from 0 to N-1.
Python was already known to be slow yet it deliberately crippled itself
by using just about the slowest method imaginable of executing a simple
iterative loop? By first creating a list of a million objects!
And sometimes you weren't even interested in the values but just wanted
to execute something N times so it was a wasted effort.
That was eventually fixed with xrange, but why do it like that in the
first place?
(At the time, I was creating bytecode languages as part of the
applications I was writing. An empty for-loop executed just one bytecode
per iteration, and it was also the fastest bytecode instruction. An
empty for-loop executed three Python bytecodes per iteration last time I
looked. It seems that Python used to like making a rod for its own back.)
--
Bartc
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