Interesting. I think I originally ripped mine off from one of the comments at:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/363051 although I've tried to make mine more readable. The thread you linked to has the apparent winner of Ron Adams: def flatten(seq): s = [] while seq: while isinstance(seq[0],list): seq = seq[0]+seq[1:] s.append(seq.pop(0)) return s But that modifies the input, which I consider to be very undesirable. The version I'm using does avoid recursive function calls. Its not clear to me at the moment how to speed it up significantly while avoiding the input modification. -Marshall On Jun 28, 3:15 pm, [EMAIL PROTECTED] wrote: > There's a good discussion on the python mailing list regarding flatten: > > http://mail.python.org/pipermail/python-list/2005-July/330367.html > > particularly, it's got a number of different implementations, and benchmarks. > > On Thu, 28 Jun 2007, Hamptonio wrote: > > > I often want to flatten nested lists, and such a command (like > > Mathematica's Flatten) does not seem to be present in sage. I propose > > adding such a command into the misc.py. I am appending some candidate > > code below, and I will also put it on sage-trac (http:// > >www.sagemath.org:9002/sage_trac/ticket/395) > > > Here's my function: > > > def flatten(in_list, ltypes=(list, tuple)): > > """ > > Flattens a nested list. > > > INPUT: > > in_list -- a list or tuple > > ltypes -- optional list of particular types to flatten > > > OUTPUT: > > a flat list of the entries of in_list > > > EXAMPLES: > > sage: flatten([[1,1],[1],2]) > > [1, 1, 1, 2] > > sage: flatten((['Hi',2,vector(QQ,[1,2,3])],(4,5,6))) > > ['Hi', 2, (1, 2, 3), 4, 5, 6] > > sage: flatten((['Hi',2,vector(QQ,[1,2,3])], > > (4,5,6)),ltypes=(list, tuple, > > sage.modules.vector_rational_dense.Vector_rational_dense)) > > ['Hi', 2, 1, 2, 3, 4, 5, 6] > > """ > > index = 0 > > new_list = [x for x in in_list] > > while index < len(new_list): > > if not new_list[index]: > > new_list.pop(index) > > continue > > while isinstance(new_list[index], ltypes): > > new_list[index : index + 1] = list(new_list[index]) > > index += 1 > > return new_list --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
