Question

I would like to match various cominations of nested matched parentheses that do not exceed a given depth.

If the depth is two, the following should match

H<>
H<a>
H<<a><b>>
H<a<b>c<d>>

These shoud not:

H<<<>>>
H<<<>><<><>><>>

I thought I would make a function that generates the regex

INNER = r"[^<>]"
OPEN  = r"<"
CLOSE = r">"

def parenthesis(depth=2):
    if depth == 0:
        return INNER
    inner = "("
    for i in range(depth):
        inner += parenthesis(i) + "|"
    inner = inner[:-1]+")*?"
    return "("+OPEN + inner + CLOSE+")"

this seems to work (though I’m not completely confident) if I do, for example:

re.match("H"+parentthesis(2), "H<<>>")

But really I want to match curley brackets that are not escaped. So:

OPEN = r"(?<!\\)[\{]"
CLOSE = r"(?<!\\)[\}]"

and, something I am unsure of:

INNER = r"[^(?<!\\)[\}\{]]"

This doesn’t seem to work. Any ideas. This is giving me a headache!

Answer 1

Try this:

INNER = r"(?:\\{|\\}|[^{}])"

It means an escaped brace, or a character that isn’t a brace.