it seems that range() can be really slow:
the following program will run, and the last line shows how long it ran
for:
import time
startTime = time.time()
a = 1.0
for i in range(0, 30000):
if i in range (0, 10000):
a += 1
if not i % 1000: print i
print a, " ", round(time.time () - startTime, 1), "seconds"
---------------------------------
the last line of output is
---------------------------------
10001.0 22.8 seconds
so if i change the line
if i in range (0, 10000):
to
if i >= 0 and i < 10000:
the the last line is
10001.0 0.2 seconds
so approximately, the program ran 100 times faster!
or is there an alternative use of range() or something similar that can
be as fast?
Jul 18 '06
45  8576 
Grant Edwards wrote:
On 2006-07-18, Marc 'BlackJack' Rintsch <bj****@gmx.net wrote:
>>In <11************ **********@h48g 2000cwc.googleg roups.com>, tac-tics
wrote:
>>>Grant Edwards wrote:
for pete's sake use the comparison operator like god intended.
if 0 <= i <= 10000:
I'm assuming you used Python's compound comparison as opposed to the
C-style of and'ing two comparisons together to emphasize the fact it is
god's chosen way of doing this ;-)
Pete doesn't like to be called god in public. ;-)
Interesting point. Does the phrase "for pete's sake as god
intended" equate pete with god?
It's possible that pete is not god and yet god's intentions are
in pete's best interest, so something could be "for pete's
sake" and "as god intended" without pete being god.
That said, "for pete's sake" is probably a just an cleaned up
version of "for god's sake", so I probably did call pete god.
No, actually you called god pete ;-)
regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden
Dan Bishop wrote:
Su************@ gmail.com wrote:
it seems that range() can be really slow:
...
if i in range (0, 10000):
This creates a 10,000-element list and sequentially searches it. Of
course that's gonna be slow.
And you're doing it 30000 times.
Nick Craig-Wood wrote:
>
Sets are pretty fast too, and have the advantage of flexibility in
that you can put any numbers in you like
I know this is self-evident to most of the people reading this, but I
thought it worth pointing out that this is a great way to test
membership in range(lo, hi, step) without doing "the necessary
algebra".
i.e. n in set(xrange(0, 10000, 23)) ...
Peace,
~Simon
Simon Forman wrote:
Nick Craig-Wood wrote:
>>
Sets are pretty fast too, and have the advantage of flexibility in
that you can put any numbers in you like
I know this is self-evident to most of the people reading this, but I
thought it worth pointing out that this is a great way to test
membership in range(lo, hi, step) without doing "the necessary
algebra".
i.e. n in set(xrange(0, 10000, 23)) ...
No, its not. It works, but it works by no means faster than
n in range(0, 10000, 23)
Both need O(n), which is a bit slow compared to
(((n - 15) % 23) == 0 and n >= 15 and n < 10000)
that will run in O(1)
Diez
Diez B. Roggisch wrote:
Simon Forman wrote:
Nick Craig-Wood wrote:
>
Sets are pretty fast too, and have the advantage of flexibility in
that you can put any numbers in you like
I know this is self-evident to most of the people reading this, but I
thought it worth pointing out that this is a great way to test
membership in range(lo, hi, step) without doing "the necessary
algebra".
i.e. n in set(xrange(0, 10000, 23)) ...
No, its not. It works, but it works by no means faster than
n in range(0, 10000, 23)
Both need O(n), which is a bit slow compared to
(((n - 15) % 23) == 0 and n >= 15 and n < 10000)
that will run in O(1)
Diez
You're right, of course. I should have said that if you're testing
such a membership, say, 30000 times AND you (like me) are slightly
rusty on the algebra and prefer to let the computer do it, then you
could use something like:
test_set = set(xrange(0, 10000, 23))
if n in test_set:
...
;-)
~Simon
Grant Edwards wrote:
>
It's unclear what you're referring to as "the range".
The notion of something describing a range of values which can be
expanded to a list or, of relevance here, whose boundaries can be
tested efficiently.
Perhaps you're thinking of a slice? Somethign like
if (0:10000).conta ins(x):
Did you mean...?
(0:10000) # SyntaxError
slice(0, 10000).contains (x) # AttributeError
3 in slice(0, 10000) # TypeError
Something like this might suffice if slice could have a __contains__
method or if people thought of slices as natural things to test
against. Perhaps we could ask the original questioner why they chose to
use range in such a way - it might indicate a background in languages
which encourage the construction of ranges and their use in comparisons
- although being told to RTFM may have scared them off.
Paul
Simon Forman wrote:
Nick Craig-Wood wrote:
>Sets are pretty fast too, and have the advantage of flexibility in
that you can put any numbers in you like
I know this is self-evident to most of the people reading this, but I
thought it worth pointing out that this is a great way to test
membership in range(lo, hi, step) without doing "the necessary
algebra".
i.e. n in set(xrange(0, 10000, 23)) ...
This is very very misleading... here are some timings :
python -mtimeit "n=5000" "n in set(xrange(0,10 000))"
1000 loops, best of 3: 1.32 msec per loop
python -mtimeit "n=5000" "n in xrange(0,10000) "
1000 loops, best of 3: 455 usec per loop
python -mtimeit "n=5000" "0 <= n < 10000"
1000000 loops, best of 3: 0.217 usec per loop
sets are fast only if you create them *once* and use them again and
again. even in that case, the sets use up O(n) memory.
with comparison operators, you don't need extra memory *and* there is no
pre-computation required.
[sreeram;]
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On 2006-07-18, Steve Holden <st***@holdenwe b.comwrote:
>That said, "for pete's sake" is probably a just an cleaned up
version of "for god's sake", so I probably did call pete god.
No, actually you called god pete ;-)
Well that's certainly wrong, because we all know god's name is
Howard.
Our father who art in heaven,
Howard be thy name,
....
--
Grant Edwards grante Yow! .. I have a
at VISION! It's a RANCID
visi.com double-FISHWICH on an
ENRICHED BUN!!
On 2006-07-18, Paul Boddie <pa**@boddie.or g.ukwrote:
>It's unclear what you're referring to as "the range".
The notion of something describing a range of values which can be
expanded to a list or, of relevance here, whose boundaries can be
tested efficiently.
>Perhaps you're thinking of a slice? Somethign like
if (0:10000).conta ins(x):
I didn't mean to imply that would actually work, but I thought
maybe that's what you were proposing.
Did you mean...?
(0:10000) # SyntaxError
slice(0, 10000).contains (x) # AttributeError
3 in slice(0, 10000) # TypeError
Something like this might suffice if slice could have a __contains__
method or if people thought of slices as natural things to test
against.
A slice seems to me to be the obvious way to represent a finite
length algebraic sequence of integers. However, obvioiusness
is in the eye of the beholder since as you point out below to
the OP, a range() was the obvious way to it.
Perhaps we could ask the original questioner why they chose to
use range in such a way - it might indicate a background in
languages which encourage the construction of ranges and their
use in comparisons - although being told to RTFM may have
scared them off.
--
Grant Edwards grante Yow! Did I say I was a
at sardine? Or a bus???
visi.com
Dan Bishop:
xrange already has __contains__. The problem is, it's implemented by a
highly-inefficient sequential search. Why not modify it to merely
check the bounds and (value - start) % step == 0?
I think this is a nice idea.
Bye,
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