code: def get_next_base26(prev=None):
      
      if not prev:
          return 'a'
  
      r = re.compile("^[a-z]*$")
      if not r.match(prev):
          raise ValueError("Invalid base26")
  
      if not prev.endswith('z'):
          return prev[:-1] + chr(ord(prev[-1]) + 1)
  
      return get_next_base26(prev[:-1]) + 'a'
docs: Increment letter-based IDs.
  
      Generates IDs like ['a', 'b', ..., 'z', 'aa', ab', ..., 'az', 'ba', ...]
  
      Returns:
          str: Next base-26 ID.