docs: def md5sum(fname, block_size=1048576):  # 2 ** 20
      """Calculate the md5sum for a file.
  
      Parameters
      ----------
      fname : str
          Filename.
      block_size : int
          Block size to use when reading.
  
      Returns
      -------
      hash_ : str
          The hexadecimal digest of the hash.
      """
      md5 = hashlib.md5()
      with open(fname, 'rb') as fid:
          while True:
              data = fid.read(block_size)
              if not data:
                  break
              md5.update(data)
      return md5.hexdigest()