"rt", "wt", "xt" or "at" for text mode.
The default mode is "rb", and the default compresslevel is 9.

For binary mode, this function is equivalent to the BZ2File
constructor: BZ2File(filename, mode, compresslevel). In this case,
the encoding, errors and newline arguments must not be provided.

For text mode, a BZ2File object is created, and wrapped in an
io.TextIOWrapper instance with the specified encoding, error
handling behavior, and line ending(s).

Z