Question

So I have a string like this:

A!
B!
C!
<tag>
D!
E!
</tag>
F!
<tag>
G!
</tag>

Is it possible to parse this with a regex so I get this output (a list):

[A, B, C, [D, E], F, [G]]

Basically I’m looking for a way to split the string by ! and by the tag…and the tag part can happen anywhere…and multiple times (but not recursively…meaning a tag within a tag…this doesn’t happen). The whole thing seems regular…is this even possible to do with regex?

EDIT: I am using Python

EDIT2: I am only using A, B, C… as a representation…those can be any string made out of letters and numbers

Answer 1

from collections import deque
from types import StringTypes

s = "A!\nB!\nC!\n<tag>\nD!\nE!\n</tag>\nF!\n<tag>\nG!\n</tag>"

def parse(parts):
    if type(parts) in StringTypes:
        parts = deque(parts.split("\n"))
    ret = []
    while parts:
        part = parts.popleft()
        if part[-1] == "!":
            ret.append(part[:-1])
        elif part == "<tag>":
            ret.append(parse(parts))
        elif part == "</tag>":
            return ret
    return ret

print parse(s)

I use a deque for speed because pop(0) would be very slow, and reversing the list and using pop() would make the function harder to read and understand.

I dare anyone to create a regexp doing the same, while also improving clarity!

(BTW, I think you could also use the pyparsing module to solve this problem, since it supports recursion.)

EDIT: Changed function to expect either string or deque as argument, simplifying invocation.