This takes a binary file for writing a pickle data stream. The optional *protocol* argument tells the pickler to use the given protocol; supported protocols are 0, 1, 2, 3, 4 and 5. The default protocol is 5. It was introduced in Python 3.8, and is incompatible with previous versions. Specifying a negative protocol version selects the highest protocol version supported. The higher the protocol used, the more recent the version of Python needed to read the pickle produced. The *file* argument must have a write() method that accepts a single bytes argument. It can thus be a file object opened for binary writing, an io.BytesIO instance, or any other custom object that meets this interface. If *fix_imports* is True and protocol is less than 3, pickle will try to map the new Python 3 names to the old module names used in Python 2, so that the pickle data stream is readable with Python 2. If *buffer_callback* is None (the default), buffer views are serialized into *file* as part of the pickle stream. If *buffer_callback* is not None, then it can be called any number of times with a buffer view. If the callback returns a false value (such as None), the given buffer is out-of-band; otherwise the buffer is serialized in-band, i.e. inside the pickle stream. It is an error if *buffer_callback* is not None and *protocol* is None or smaller than 5.