class_docstr: Generic matlab matrix writing class 
class_docstr_tok: ["Generic","matlab","matrix","writing","class"]
code: def update_matrix_tag(self, start_pos):
      curr_pos = self.file_stream.tell()
      self.file_stream.seek(start_pos)
      byte_count = curr_pos - start_pos - 8
      if byte_count >= 2**32:
          raise MatWriteError(
              "Matrix too large to save with Matlab " "5 format"
          )
      self.mat_tag["byte_count"] = byte_count
      self.write_bytes(self.mat_tag)
      self.file_stream.seek(curr_pos)
  
imports: from __future__ import division, print_function, absolute_import
  import os
  import time
  import sys
  import zlib
  from io import BytesIO
  import warnings
  import numpy
  from numpy.compat import asbytes, asstr
  import scipy.sparse
  from scipy._lib.six import string_types
  from .byteordercodes import native_code, swapped_code
  from .miobase import MatFileReader, docfiller, matdims, read_dtype, arr_to_chars, arr_dtype_number, MatWriteError, MatReadError, MatReadWarning
  from .mio5_utils import VarReader5
  from .mio5_params import MatlabObject, MatlabFunction, MDTYPES, NP_TO_MTYPES, NP_TO_MXTYPES, miCOMPRESSED, miMATRIX, miINT8, miUTF8, miUINT32, mxCELL_CLASS, mxSTRUCT_CLASS, mxOBJECT_CLASS, mxCHAR_CLASS, mxSPARSE_CLASS, mxDOUBLE_CLASS, mclass_info
  from .streams import ZlibInputStream
label_desc: Use image node_id 8 for calling the VarWriter5 obj's underlying member method code with example usage: obj.update_matrix_tag(start_pos) without return types