parser.py

def f(l, o='{}'):
  s=[[]]
  def x(): s[-1].append([]); s.append(s[-1][-1])
  def y(): return -1 if len(s) == 1 else s.pop()
  for c in l:
    try:
      if { o[0]: x, o[1]: y }[c]() == -1: return False
    except KeyError: s[-1].append(c)
  return s[0] if len(s) == 1 else False