code: def _read_string_data(f):
      """Read a data string (length is specified twice)"""
      length = _read_long(f)
      if length > 0:
          length = _read_long(f)
          string_data = _read_bytes(f, length)
          _align_32(f)
      else:
          string_data = ""
      return string_data
  
imports: import struct
  import numpy
  import tempfile
  import zlib
  import warnings
label_desc: Use image node_id 15 for calling a global function with example usage: _read_string_data(f) and returns: string_data