docs: def get_file_checksum(path):
      """Get the checksum of a file (using ``sum``, Unix-only).
  
      This function is only available on certain platforms.
  
      Parameters
      ----------
      path: str
          The path of the file.
  
      Returns
      -------
      int
          The checksum.
  
      Raises
      ------
      IOError
          If the file does not exist.
      """
  
      if not (sys.platform.startswith('linux') or \
                          sys.platform in ['darwin', 'cygwin']):
          raise OSError('This function is not available on your platform.')
  
      assert isinstance(path, (str, _oldstr))
  
      if not os.path.isfile(path): # not a file
          raise IOError('File "%s" does not exist.' %(path))
  
      # calculate checksum
      sub = subproc.Popen('sum "%s"' %(path), bufsize=-1, shell=True,
                          stdout=subproc.PIPE)
      stdoutdata = sub.communicate()[0]
      assert sub.returncode == 0
  
      # in Python 3, communicate() returns bytes that need to be decoded
      encoding = locale.getpreferredencoding()
      stdoutstr = str(stdoutdata, encoding=encoding)
  
      file_checksum = int(stdoutstr.split(' ')[0])
      logger.debug('Checksum of file "%s": %d', path, file_checksum)
      return file_checksum