code: def _infer_sig_len(file_name, fmt, n_sig, dir_name, pb_dir=None):
      
      if pb_dir is None:
          file_size = os.path.getsize(os.path.join(dir_name, file_name))
      else:
          file_size = download._remote_file_size(file_name=file_name,
                                                 pb_dir=pb_dir)
  
      sig_len = int(file_size / (BYTES_PER_SAMPLE[fmt] * n_sig))
  
      return sig_len
docs: Infer the length of a signal from a dat file.
  
      Parameters
      ----------
      file_name : str
          Name of the dat file
      fmt : str
          WFDB fmt of the dat file
      n_sig : int
          Number of signals contained in the dat file
  
      Notes
      -----
      sig_len * n_sig * bytes_per_sample == file_size