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.
- Protocol version 0 is the original ASCII protocol and is backwards compatible with
earlier versions of Python.
- Protocol version 1 is the old binary format which is also compatible with earlier
versions of Python.
- Protocol version 2 was introduced in Python 2.3. It provides much more efficient
pickling of new-style classes.
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: The bin parameter is
deprecated and only provided for backwards compatibility. You should use the protocol
A binary format, which is slightly more efficient, can be chosen by specifying a true value
for the bin argument to the Pickler constructor or the dump() and dumps() functions. A protocol
version >= 1 implies use of a binary format.