curly.py

#!/usr/bin/env python3
# https://codegolf.stackexchange.com/questions/57891/curly-numbers

import re
import math

CURLIES = [
    "{;;}", # 8
    "{{;};};", # 21
    "{};;;", # 3
    "{{{{;}}};}", # 260
    "{}", # 0
    "{};;;;;", # 5
    "{{;;;;};;}", # 72
    "c{u;r;l}y;!", # 9
    "42{;} ;;;;" # 8
]

NUMBERS = [
    4,
    17,
    1,
    0,
    96,
    100,
    112,
    123
]

def un_curl(curled):
    curled = ''.join(re.findall('[{};]', curled))

    # store the previous character
    last = None
    # final result
    num = 0
    # stack for braces
    stack = 0

    if curled[0] != '{':
        return False

    for c in curled:
        if c == '{':
            # braces cannot be touching, and semicolon can't be next to group
            if last == '}' or last == ';':
                return False
            stack += 1
        elif c == '}':
            num *= 4
            stack -= 1
        elif c == ';':
            num += 1

        last = c

    # make sure all of the braces have been closed
    return num if stack == 0 else False

def curl(num):
    curled = ''
    braces = 0

    # fuck you
    if num == 1:
        return '{};'
    elif num == 0:
        return '{}'

    while num > 0:
        curled = (num % 4 * ';') + curled
        if num > 1:
            curled = '}' + curled
            braces += 1
        num = math.floor(num / 4)

    return (braces * '{') + curled

[print(curly, un_curl(curly)) for curly in CURLIES]
[print(num, curl(num)) for num in NUMBERS]