Op 2005-12-20, [EMAIL PROTECTED] schreef <[EMAIL PROTECTED]>: > What I would like to see supported is > the concept that enumerate should give indices and items from an > iterable--it does right now--but it should also allow you to access a > different portion of the original list and *still* give the indices of > that slice. What I propose is an optional slice argument that would be > used to return the sliced indices and items: > > def enum(l, slc=None): > if slc==None: #the usual ennumerate > for i, dat in enumerate(l): > yield i, dat > else: > if type(slc)<>slice: > raise TypeError, "slc must be a valid slice" > start, step = slc.start, slc.step > # > # we need actual values for start and step, so check for None > # and supply defaults > # > if step==None:step=1 > if start==None: > if step>0: > start=0 > else: > start=-1 > for i, dat in enumerate(l[slc]): > j = i*step+start > if j<0: j+=len(l) #always give positive indices > yield j, dat > ### >>>> for i, x in enum(range(10), slice(start, start+count)):
The trouble with your suggestion (and the original enumerate, which you rely on if no slice is provided) is that it doesn't work as desired if you just give it a sequence that starts at an other index than zero. I have a table modules, tables are similar to lists but they can start at arbitrary indexes. So if I have a table that goes from -4 to +4, I would like enumerate(tab) or enum(tab) to give me: (-4, tab[-4]) (-3, tab[-3]) ... Of course this needs some cooperation from the sequence type. Personnaly I would have though of a range method on the sequence which could be used by enumerate to know where to start and end. I also would prefer the possibilty to use the same notation as with sequence subscription instead of having to use the cumbersome slice notation. Something like: enum(lst, start:start+count) Instead of enum(lst, slice(start, start+count)) Of course if you wouldn't mind brackets instead of parenthesis we could implement enum as a vitual slice, we then would have to write: enum[lst, start:start+count] Just my 2 cents. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
