code: def parse(cls, fptr, offset, length):
          
          read_buffer = fptr.read(4)
          signature = struct.unpack('>BBBB', read_buffer)
  
          return cls(signature=signature, length=length, offset=offset)
docs: Parse JPEG 2000 signature box.
  
          Parameters
          ----------
          fptr : file
              Open file object.
          offset : int
              Start position of box in bytes.
          length : int
              Length of the box in bytes.
  
          Returns
          -------
          JPEG2000SignatureBox
              Instance of the current JPEG2000 signature box.