Neil Cerutti wrote: > On 2013-08-28, John Levine <jo...@iecc.com> wrote: >> I have a crufty old DNS provisioning system that I'm rewriting and I >> hope improving in python. (It's based on tinydns if you know what >> that is.) >> >> The record formats are, in the worst case, like this: >> >> foo.[DOM]::[IP6::4361:6368:6574]:600:: >> >> What I would like to do is to split this string into a list like this: >> >> [ 'foo.[DOM]','','[IP6::4361:6368:6574]','600','' ] >> >> Colons are separators except when they're inside square >> brackets. I have been messing around with re.split() and >> re.findall() and haven't been able to come up with either a >> working separator pattern for split() or a working field >> pattern for findall(). I came pretty close with findall() but >> can't get it to reliably match the nothing between two adjacent >> colons not inside brackets. >> >> Any suggestions? I realize I could do it in a loop where I pick >> stuff off the front of the string, but yuck. > > A little parser, as Skip suggested, is a good way to go. > > The brackets make your string context-sensitive, a difficult > concept to cleanly parse with a regex. > > I initially hoped a csv module dialect could work, but the quote > character is (currently) hard-coded to be a single, simple > character, i.e., I can't tell it to treat [xxx] as "xxx". > > What about Skip's suggestion? A little parser. It might seem > crass or something, but it really is easier than musceling a > regex into a context sensitive grammer. > > def dns_split(s): > in_brackets = False > b = 0 # index of beginning of current string > for i, c in enumerate(s): > if not in_brackets: > if c == "[": > in_brackets = True > elif c == ':': > yield s[b:i] > b = i+1 > elif c == "]": > in_brackets = False
I think you need one more yield outside the loop. >>>> print(list(dns_split(s))) > ['foo.[DOM]', '', '[IP6::4361:6368:6574]', '600', ''] > > It'll gag on nested brackets (fixable with a counter) and has no > error handling (requires thought), but it's a start. Something similar on top of regex: >>> def split(s): ... start = level = 0 ... for m in re.compile(r"[[:\]]").finditer(s): ... if m.group() == "[": level += 1 ... elif m.group() == "]": ... assert level ... level -= 1 ... elif level == 0: ... yield s[start:m.start()] ... start = m.end() ... yield s[start:] ... >>> list(split("a[b:c:]:d")) ['a[b:c:]', 'd'] >>> list(split("a[b:c[:]]:d")) ['a[b:c[:]]', 'd'] >>> list(split("")) [''] >>> list(split(":")) ['', ''] >>> list(split(":x")) ['', 'x'] >>> list(split("[:x]")) ['[:x]'] >>> list(split(":[:x]")) ['', '[:x]'] >>> list(split(":[:[:]:x]")) ['', '[:[:]:x]'] >>> list(split("[:::]")) ['[:::]'] >>> s = "foo.[DOM]::[IP6::4361:6368:6574]:600::" >>> list(split(s)) ['foo.[DOM]', '', '[IP6::4361:6368:6574]', '600', '', ''] Note that there is one more empty string which I believe the OP forgot. -- http://mail.python.org/mailman/listinfo/python-list