code: def bytesio_filemap(klass):
      """Return bytes io filemap for this image class `klass`"""
      file_map = klass.make_file_map()
      for name, fileholder in file_map.items():
          fileholder.fileobj = BytesIO()
          fileholder.pos = 0
      return file_map
  
imports: from io import BytesIO
  import numpy
  from ..optpkg import optional_package
  from numpy.testing import assert_array_equal
label_desc: Use image node_id 1 for calling a global function with example usage: bytesio_filemap(klass) and returns: file_map