> I would like to search for a substring in a string and get the index of > all occurances. > > mystring = 'John has a really nice powerbook.' > substr = ' ' # space > > I would like to get this list: > [4, 8, 10, 17, 22] > > How can I do that without using "for i in mystring" which might be > expensive for large strings?
>>> mystring = 'John has a really nice powerbook.' >>> substr = ' ' >>> indicies = [i for i in xrange(len(mystring)) if mystring.startswith(substr, i)] >>> indicies [4, 8, 10, 17, 22] is my preferred way of doing this. Theoretically, it doesn't involve copying any bits of the string, as startswith(substring, offset) *should* be smart enough to do the check internally without copying pieces of mystring for comparison, just to return whether a submatch starts there. Whether it *does* do that is another matter for the higher python powers. It also uses xrange which shouldn't create a temporary array of indicies, but rather use an iteratable sequence generator. It should work for finding all 3 instances of "aba' in "abababa" as well, another common query of a similar form here on the list. -tkc -- http://mail.python.org/mailman/listinfo/python-list
