Re: A little more advanced for loop
In article <[EMAIL PROTECTED]>, Larry Bates <[EMAIL PROTECTED]> wrote: > >Note: if lists are long take a look at itertools izip. zip creates >a list of lists which could take lots of memory/time if they are VERY >large. itertools izip iterates over them in place. That's half-true -- while izip is faster, it's not enough faster to make a significant difference unless the lists are "huge" rather than "large". Remember that the data elements themselves are not copied. -- Aahz ([EMAIL PROTECTED]) <*> http://www.pythoncraft.com/ "I disrespectfully agree." --SJM -- http://mail.python.org/mailman/listinfo/python-list
Re: A little more advanced for loop
Larry Bates <[EMAIL PROTECTED]> wrote: > Note: if lists are long take a look at itertools izip. zip creates > a list of lists which could take lots of memory/time if they are VERY > large. itertools izip iterates over them in place. That's interesting. I was going to quibble with the assertion that zip could take lots of time, since on the face of it a loop using izip packs and unpacks just as many tuples. Fortunately I tried it out before claiming that zip would be just as fast :) It would appear that even for short sequences the izip solution is faster. My guess would be it is because the same tuple objects are being reused in the izip version. C:\Python25\Lib>timeit.py -s "a, b, c = [range(1000)]*3" -s "from itertools import izip" "for p,q,r in izip(a,b,c): pass" 1 loops, best of 3: 131 usec per loop C:\Python25\Lib>timeit.py -s "a, b, c = [range(1000)]*3" "for p,q,r in zip(a,b,c): pass" 1000 loops, best of 3: 212 usec per loop C:\Python25\Lib>timeit.py -s "a, b, c = [range(100)]*3" -s "from itertools import izip" "for p,q,r in izip(a,b,c): pass" 10 loops, best of 3: 13.9 usec per loop C:\Python25\Lib>timeit.py -s "a, b, c = [range(100)]*3" "for p,q,r in zip(a,b,c): pass" 1 loops, best of 3: 22.6 usec per loop C:\Python25\Lib>timeit.py -s "a, b, c = [range(10)]*3" -s "from itertools import izip" "for p,q,r in izip(a,b,c): pass" 10 loops, best of 3: 2.21 usec per loop C:\Python25\Lib>timeit.py -s "a, b, c = [range(10)]*3" "for p,q,r in zip(a,b,c): pass" 10 loops, best of 3: 3.52 usec per loop -- http://mail.python.org/mailman/listinfo/python-list
Re: A little more advanced for loop
Horta wrote: > On Feb 9, 9:00 am, Stephan Diehl <[EMAIL PROTECTED]> wrote: >> Horta wrote: >>> Hi folks, >>> Suppose I have to loop over 3 lists being the same size at the same >>> time and order. How can I do that without using the range() function >>> or whatever indexing? >>> Example using range: >>> a = ['aaa', ''] >>> b = ['bb', ''] >>> c = ['c', ''] >>> for i in range(len(a)): >>> # using a[i], b[i], and c[i] >>> I'm sure there's a elegant way to do that... >>> Thanks in advance. >> Sure, there is: >> >> for a_item, b_item , c_item in zip(a,b,c): >> # do something > > Thanks guys! > Note: if lists are long take a look at itertools izip. zip creates a list of lists which could take lots of memory/time if they are VERY large. itertools izip iterates over them in place. from itertools import izip for a_item, b_item, c_item in izip(a,b,c): # do something -Larry -- http://mail.python.org/mailman/listinfo/python-list
Re: A little more advanced for loop
On Feb 9, 9:00 am, Stephan Diehl <[EMAIL PROTECTED]> wrote: > Horta wrote: > > Hi folks, > > > Suppose I have to loop over 3 lists being the same size at the same > > time and order. How can I do that without using the range() function > > or whatever indexing? > > > Example using range: > > > a = ['aaa', ''] > > b = ['bb', ''] > > c = ['c', ''] > > > for i in range(len(a)): > > # using a[i], b[i], and c[i] > > > I'm sure there's a elegant way to do that... > > > Thanks in advance. > > Sure, there is: > > for a_item, b_item , c_item in zip(a,b,c): > # do something Thanks guys! -- http://mail.python.org/mailman/listinfo/python-list
Re: A little more advanced for loop
Horta wrote: > Hi folks, > > Suppose I have to loop over 3 lists being the same size at the same > time and order. How can I do that without using the range() function > or whatever indexing? > > Example using range: > > a = ['aaa', ''] > b = ['bb', ''] > c = ['c', ''] > > for i in range(len(a)): > # using a[i], b[i], and c[i] > > I'm sure there's a elegant way to do that... > > Thanks in advance. > Sure, there is: for a_item, b_item , c_item in zip(a,b,c): # do something -- http://mail.python.org/mailman/listinfo/python-list
Re: A little more advanced for loop
Horta wrote: > Hi folks, > > Suppose I have to loop over 3 lists being the same size at the same > time and order. How can I do that without using the range() function > or whatever indexing? > > Example using range: > > a = ['aaa', ''] > b = ['bb', ''] > c = ['c', ''] > > for i in range(len(a)): > # using a[i], b[i], and c[i] > > I'm sure there's a elegant way to do that... Use zip: for av, bv, cv in zip(a, b, c): print av, bv, cv Diez -- http://mail.python.org/mailman/listinfo/python-list
