range() is not the best way to check range?

[Summercoolness]

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?

[Dan Bishop]

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.

[Leif K-Brooks]

Su************@ gmail.com wrote:

or is there an alternative use of range() or something similar that can
be as fast?

You could use xrange:

leif@ubuntu:~$ python -m timeit -n10000 "1 in range(10000)"
10000 loops, best of 3: 260 usec per loop
leif@ubuntu:~$ python -m timeit -n10000 "1 in xrange(10000)"
10000 loops, best of 3: 0.664 usec per loop

[Dan Bishop]

Leif K-Brooks wrote:

Su************@ gmail.com wrote:

or is there an alternative use of range() or something similar that can
be as fast?

You could use xrange:

leif@ubuntu:~$ python -m timeit -n10000 "1 in range(10000)"
10000 loops, best of 3: 260 usec per loop
leif@ubuntu:~$ python -m timeit -n10000 "1 in xrange(10000)"
10000 loops, best of 3: 0.664 usec per loop

That's only because you're choosing a number that's early in the list.

~$ python -m timeit -n10000 "1 in xrange(10000)"
10000 loops, best of 3: 1.22 usec per loop
~$ python -m timeit -n10000 "9999 in xrange(10000)"
10000 loops, best of 3: 1.24 msec per loop

That's *milliseconds*, not microseconds.

[John Machin]

On 18/07/2006 12:41 PM, Su************@ gmail.com wrote:

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?

Some things to try:
1a. Read what the manual has to say about the range() function ... what
does it produce?

1b. Read what the manual has to say about time.time() and time.clock().
Change over to using time.clock(). Change the round(...., 1) to (say) 4.

Alternatively, use something like this:

print "%.1f ... %.4f seconds" % (a, time.clock() - startTime)

1c. Repeat the two ways that you tried already.

2. First alternative:

Do this:

test_range = range(10000)

*once*, just after "a = 1.0".

and change your if test to

if i in test_range:

3. Now change that to:

test_range = set(range(10000 ))

4. Now forget about test_range, and change your if test to this:

if 0 <= i < 10000:

HTH,
John

[K.S.Sreeram]

Su************@ gmail.com wrote:

so if i change the line
if i in range (0, 10000):
to
if i >= 0 and i < 10000:

[snip;]

is there an alternative use of range() or something similar that can
be as fast?

you've found that alternative yourself! just use the comparison operators...

in fact, you can write a little more compact as:
if 0 <= i < 10000 :
[sreeram;]
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Version: GnuPG v1.4.2.2 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFEvFGdrgn 0plK5qqURAlXhAJ 9mrod2ofLGlSCks nXqjzWDd0Y35wCg tx0f
+Fn3h07cOFT16Nv CX+DDqnY=
=Hk3J
-----END PGP SIGNATURE-----

[Grant Edwards]

On 2006-07-18, Su************@ gmail.com <Su************ @gmail.comwrote :

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"

or is there an alternative use of range() or something similar that can
be as fast?

Creating and then searching a 10,000 element list to see if a
number is between two other numbers is insane.

Using xrange as somebody else suggested is also insane.

If you want to know if a number is between two other numders,
for pete's sake use the comparison operator like god intended.

if 0 <= i <= 10000:

--
Grant Edwards grante Yow! ANN JILLIAN'S HAIR
at makes LONI ANDERSON'S
visi.com HAIR look like RICARDO
MONTALBAN'S HAIR!

[tac-tics]

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 ;-)

[Marc 'BlackJack' Rintsch]

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. ;-)

Ciao,
Marc 'BlackJack' Rintsch

[Nick Craig-Wood]

Grant Edwards <gr****@visi.co mwrote:

Creating and then searching a 10,000 element list to see if a
number is between two other numbers is insane.

Using xrange as somebody else suggested is also insane.

Aye to both

If you want to know if a number is between two other numders,
for pete's sake use the comparison operator like god intended.

if 0 <= i <= 10000:

Sets are pretty fast too, and have the advantage of flexibility in
that you can put any numbers in you like

$ python2.4 -m timeit -s 's=range(0,1000 0); i=5000' 'i in s'
1000 loops, best of 3: 228 usec per loop

$ python2.4 -m timeit -s 's=set(range(0, 10000)); i=5000' 'i in s'
1000000 loops, best of 3: 0.312 usec per loop

$ python2.4 -m timeit -s 'i=5000' '0 <= i < 10000'
1000000 loops, best of 3: 0.289 usec per loop

The below prints

range) That took 21.512 seconds: result 10001.0
set) That took 0.023 seconds: result 10001.0
comparison) That took 0.024 seconds: result 10001.0

............... ............... ............... ............... .

import time

start = time.time()
a = 1.0
for i in range(0, 30000):
if i in range(0, 10000):
a += 1
dt = time.time() - start
print "range) That took %.3f seconds: result %s" % (dt, a)

start = time.time()
a = 1.0
mine = set(range(0, 10000))
for i in range(0, 30000):
if i in mine:
a += 1
dt = time.time() - start
print "set) That took %.3f seconds: result %s" % (dt, a)

start = time.time()
a = 1.0
mine = set(range(0, 10000))
for i in range(0, 30000):
if 0 <= i < 10000:
a += 1
dt = time.time() - start
print "comparison ) That took %.3f seconds: result %s" % (dt, a)

--
Nick Craig-Wood <ni**@craig-wood.com-- http://www.craig-wood.com/nick