The data format used by pickle is Python-specific. This has the advantage that there are no restrictions imposed by external standards such as XDR (which can't represent pointer sharing); however it means that non-Python programs may not be able to reconstruct pickled Python objects.
By default, the pickle data format uses a printable ASCII representation. This is slightly more voluminous than a binary representation. The big advantage of using printable ASCII (and of some other characteristics of pickle's representation) is that for debugging or recovery purposes it is possible for a human to read the pickled file with a standard text editor.
There are currently 3 different protocols which can be used for pickling.
Refer to PEP 307 for more information.
If a protocol is not specified, protocol 0 is used. If protocol is specified as a negative value or HIGHEST_PROTOCOL, the highest protocol version available will be used.
Changed in version 2.3: Introduced the protocol parameter.
A binary format, which is slightly more efficient, can be chosen by specifying a protocol version >= 1.
See About this document... for information on suggesting changes.