13.1.2 Data stream format
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: Introduced the protocol parameter.
A binary format, which is slightly more efficient, can be chosen by specifying a protocol version >= 1.
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Release 2.5, documentation updated on 19th September, 2006.