code: def _open(self):
      # check header
      n = 27 * 4  # read 27 float values
      f = self.fp.read(n)
  
      try:
          self.bigendian = 1
          t = struct.unpack(">27f", f)  # try big-endian first
          hdrlen = isSpiderHeader(t)
          if hdrlen == 0:
              self.bigendian = 0
              t = struct.unpack("<27f", f)  # little-endian
              hdrlen = isSpiderHeader(t)
          if hdrlen == 0:
              raise SyntaxError("not a valid Spider file")
      except struct.error:
          raise SyntaxError("not a valid Spider file")
  
      h = (99,) + t  # add 1 value : spider header index starts at 1
      iform = int(h[5])
      if iform != 1:
          raise SyntaxError("not a Spider 2D image")
  
      self._size = int(h[12]), int(
          h[2]
      )  # size in pixels (width, height)
      self.istack = int(h[24])
      self.imgnumber = int(h[27])
  
      if self.istack == 0 and self.imgnumber == 0:
          # stk=0, img=0: a regular 2D image
          offset = hdrlen
          self._nimages = 1
      elif self.istack > 0 and self.imgnumber == 0:
          # stk>0, img=0: Opening the stack for the first time
          self.imgbytes = int(h[12]) * int(h[2]) * 4
          self.hdrlen = hdrlen
          self._nimages = int(h[26])
          # Point to the first image in the stack
          offset = hdrlen * 2
          self.imgnumber = 1
      elif self.istack == 0 and self.imgnumber > 0:
          # stk=0, img>0: an image within the stack
          offset = hdrlen + self.stkoffset
          self.istack = 2  # So Image knows it's still a stack
      else:
          raise SyntaxError("inconsistent stack header values")
  
      if self.bigendian:
          self.rawmode = "F;32BF"
      else:
          self.rawmode = "F;32F"
      self.mode = "F"
  
      self.tile = [
          ("raw", (0, 0) + self.size, offset, (self.rawmode, 0, 1))
      ]
      self.__fp = self.fp
  
imports: from __future__ import print_function
  import os
  import struct
  import sys
  from PIL import Image, ImageFile
label_desc: Use image node_id 1 for calling the SpiderImageFile obj's underlying member method code with example usage: obj._open() without return types