bpo-23403: Bump pickle.DEFAULT_PROTOCOL to 4 (#6355) · pythoncapi/cpython@c51d8c9 · GitHub
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bpo-23403: Bump pickle.DEFAULT_PROTOCOL to 4 (python#6355)
This makes performance better and produces shorter pickles. This change is backwards compatible up to the oldest currently supported version of Python (3.4).
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‎Doc/library/pickle.rst‎

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‎Doc/whatsnew/3.8.rst‎

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@@ -94,6 +94,9 @@ Improved Modules
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Optimizations
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=============
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* The default protocol in the :mod:`pickle` module is now Protocol 4,
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first introduced in Python 3.4. It offers better performance and smaller
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size compared to Protocol 3 available since Python 3.0.
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Build and C API Changes
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=======================

‎Lib/pickle.py‎

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@@ -57,9 +57,9 @@
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HIGHEST_PROTOCOL = 4
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# The protocol we write by default. May be less than HIGHEST_PROTOCOL.
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# We intentionally write a protocol that Python 2.x cannot read;
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# there are too many issues with that.
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DEFAULT_PROTOCOL = 3
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# Only bump this if the oldest still supported version of Python already
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# includes it.
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DEFAULT_PROTOCOL = 4
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class PickleError(Exception):
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"""A common base class for the other pickling exceptions."""
@@ -376,8 +376,8 @@ def __init__(self, file, protocol=None, *, fix_imports=True):
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The optional *protocol* argument tells the pickler to use the
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given protocol; supported protocols are 0, 1, 2, 3 and 4. The
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default protocol is 3; a backward-incompatible protocol designed
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for Python 3.
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default protocol is 4. It was introduced in Python 3.4, it is
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incompatible with previous versions.
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Specifying a negative protocol version selects the highest
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protocol version supported. The higher the protocol used, the

‎Misc/NEWS.d/next/Library/2018-04-02-16-10-12.bpo-23403.KG7ADV.rst‎

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``DEFAULT_PROTOCOL`` in :mod:`pickle` was bumped to 4. Protocol 4 is
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described in :pep:`3154` and available since Python 3.4. It offers
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better performance and smaller size compared to protocol 3 introduced
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in Python 3.0.

‎Modules/_pickle.c‎

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@@ -20,10 +20,12 @@ class _pickle.UnpicklerMemoProxy "UnpicklerMemoProxyObject *" "&UnpicklerMemoPro
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[clinic start generated code]*/
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/*[clinic end generated code: output=da39a3ee5e6b4b0d input=4b3e113468a58e6c]*/
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/* Bump this when new opcodes are added to the pickle protocol. */
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/* Bump HIGHEST_PROTOCOL when new opcodes are added to the pickle protocol.
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Bump DEFAULT_PROTOCOL only when the oldest still supported version of Python
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already includes it. */
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enum {
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HIGHEST_PROTOCOL = 4,
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DEFAULT_PROTOCOL = 3
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DEFAULT_PROTOCOL = 4
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};
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/* Pickle opcodes. These must be kept updated with pickle.py.
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be more efficient.
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The optional *protocol* argument tells the pickler to use the given
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protocol supported protocols are 0, 1, 2, 3 and 4. The default
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protocol is 3; a backward-incompatible protocol designed for Python 3.
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protocol; supported protocols are 0, 1, 2, 3 and 4. The default
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protocol is 4. It was introduced in Python 3.4, it is incompatible
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with previous versions.
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Specifying a negative protocol version selects the highest protocol
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version supported. The higher the protocol used, the more recent the
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static PyObject *
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_pickle_dump_impl(PyObject *module, PyObject *obj, PyObject *file,
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PyObject *protocol, int fix_imports)
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/*[clinic end generated code: output=a4774d5fde7d34de input=830f8a64cef6f042]*/
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/*[clinic end generated code: output=a4774d5fde7d34de input=93f1408489a87472]*/
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{
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PicklerObject *pickler = _Pickler_New();
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The optional *protocol* argument tells the pickler to use the given
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protocol; supported protocols are 0, 1, 2, 3 and 4. The default
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protocol is 3; a backward-incompatible protocol designed for Python 3.
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protocol is 4. It was introduced in Python 3.4, it is incompatible
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with previous versions.
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Specifying a negative protocol version selects the highest protocol
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version supported. The higher the protocol used, the more recent the
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static PyObject *
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_pickle_dumps_impl(PyObject *module, PyObject *obj, PyObject *protocol,
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int fix_imports)
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/*[clinic end generated code: output=d75d5cda456fd261 input=293dbeda181580b7]*/
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/*[clinic end generated code: output=d75d5cda456fd261 input=b6efb45a7d19b5ab]*/
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{
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PyObject *result;
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PicklerObject *pickler = _Pickler_New();

‎Modules/clinic/_pickle.c.h‎

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