On Sat, 05 Sep 2009 23:54:08 +0100, per <perfr...@gmail.com> wrote:
On Sep 5, 6:42 pm, "Rhodri James" <rho...@wildebst.demon.co.uk> wrote:On Sat, 05 Sep 2009 22:54:41 +0100, per <perfr...@gmail.com> wrote: > I'm trying to efficiently "split" strings based on what substrings > they are made up of. > i have a set of strings that are comprised of known substrings. > For example, a, b, and c are substrings that are not identical to each > other, e.g.: > a = "0" * 5 > b = "1" * 5 > c = "2" * 5 > Then my_string might be: > my_string = a + b + c > i am looking for an efficient way to solve the following problem. > suppose i have a short > string x that is a substring of my_string. I want to "split" the > string x into blocks based on > what substrings (i.e. a, b, or c) chunks of s fall into. > to illustrate this, suppose x = "00111". Then I can detect where x > starts in my_string > using my_string.find(x). But I don't know how to partition x into > blocks depending > on the substrings. What I want to get out in this case is: "00", > "111". If x were "001111122", > I'd want to get out "00","11111", "22". > is there an easy way to do this? i can't simply split x on a, b, or c > because these might > not be contained in x. I want to avoid doing something inefficient > like looking at all substrings > of my_string etc. > i wouldn't mind using regular expressions for this but i cannot think > of an easy regular > expression for this problem. I looked at the string module in the > library but did not see > anything that seemd related but i might have missed it. I'm not sure I understand your question exactly. You seem to imply that the order of the substrings of x is consistent. If that's the case, this ought to help: >>> import re >>> x = "001111122" >>> m = re.match(r"(0*)(1*)(2*)", x) >>> m.groups() ('00', '11111', '22')>>> y = "00111" >>> m = re.match(r"(0*)(1*)(2*)", y) >>> m.groups() ('00', '111', '') You'll have to filter out the empty groups for yourself, but that's no great problem.The order of the substrings is consistent but what if it's not 0, 1, 2 but a more complicated string? e.g. a = 1030405, b = 1babcf, c = fUUIUP then the substring x might be 4051ba, in which case using a regexp with (1*) will not work since both a and b substrings begin with the character 1.
Right. This looks approximately nothing like what I thought your problem was. Would I be right in thinking that you want to match substrings of your potential "substrings" against the string x? I'm sufficiently confused that I think I'd like to see what your use case actually is before I make more of a fool of myself. -- Rhodri James *-* Wildebeest Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
