bpo-39426: Fix outdated default and highest protocols in docs (GH-18154)

Some portions of the pickle documentation hadn't been updated for the pickle protocol changes in Python 3.8 (new protocol 5, default protocol 4). This PR fixes those docs.

https://bugs.python.org/issue39426
(cherry picked from commit e9652e8)

Co-authored-by: Mark Dickinson <[email protected]>

Author: miss-islington

Lib/pickle.py

@@ -409,9 +409,9 @@ def __init__(self, file, protocol=None, *, fix_imports=True,
         """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 and 4.  The
-        default protocol is 4. It was introduced in Python 3.4, it is
-        incompatible with previous versions.
+        given protocol; supported protocols are 0, 1, 2, 3, 4 and 5.
+        The default protocol is 4. It was introduced in Python 3.4, and
+        is incompatible with previous versions.
 
         Specifying a negative protocol version selects the highest
         protocol version supported.  The higher the protocol used, the

Modules/_pickle.c

@@ -4647,8 +4647,9 @@ _pickle.Pickler.__init__
 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 and 4.  The default
-protocol is 3; a backward-incompatible protocol designed for Python 3.
+protocol; supported protocols are 0, 1, 2, 3, 4 and 5.  The default
+protocol is 4. It was introduced in Python 3.4, 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
@@ -4680,7 +4681,7 @@ static int
 _pickle_Pickler___init___impl(PicklerObject *self, PyObject *file,
                               PyObject *protocol, int fix_imports,
                               PyObject *buffer_callback)
-/*[clinic end generated code: output=0abedc50590d259b input=bb886e00443a7811]*/
+/*[clinic end generated code: output=0abedc50590d259b input=a7c969699bf5dad3]*/
 {
     _Py_IDENTIFIER(persistent_id);
     _Py_IDENTIFIER(dispatch_table);
@@ -7633,8 +7634,8 @@ This is equivalent to ``Pickler(file, protocol).dump(obj)``, but may
 be more efficient.
 
 The optional *protocol* argument tells the pickler to use the given
-protocol; supported protocols are 0, 1, 2, 3 and 4.  The default
-protocol is 4. It was introduced in Python 3.4, it is incompatible
+protocol; supported protocols are 0, 1, 2, 3, 4 and 5.  The default
+protocol is 4. It was introduced in Python 3.4, and is incompatible
 with previous versions.
 
 Specifying a negative protocol version selects the highest protocol
@@ -7660,7 +7661,7 @@ static PyObject *
 _pickle_dump_impl(PyObject *module, PyObject *obj, PyObject *file,
                   PyObject *protocol, int fix_imports,
                   PyObject *buffer_callback)
-/*[clinic end generated code: output=706186dba996490c input=cfdcaf573ed6e46c]*/
+/*[clinic end generated code: output=706186dba996490c input=5ed6653da99cd97c]*/
 {
     PicklerObject *pickler = _Pickler_New();
 
@@ -7703,8 +7704,8 @@ _pickle.dumps
 Return the pickled representation of the object as a bytes object.
 
 The optional *protocol* argument tells the pickler to use the given
-protocol; supported protocols are 0, 1, 2, 3 and 4.  The default
-protocol is 4. It was introduced in Python 3.4, it is incompatible
+protocol; supported protocols are 0, 1, 2, 3, 4 and 5.  The default
+protocol is 4. It was introduced in Python 3.4, and is incompatible
 with previous versions.
 
 Specifying a negative protocol version selects the highest protocol
@@ -7724,7 +7725,7 @@ into *file* as part of the pickle stream.  It is an error if
 static PyObject *
 _pickle_dumps_impl(PyObject *module, PyObject *obj, PyObject *protocol,
                    int fix_imports, PyObject *buffer_callback)
-/*[clinic end generated code: output=fbab0093a5580fdf input=9f334d535ff7194f]*/
+/*[clinic end generated code: output=fbab0093a5580fdf input=e543272436c6f987]*/
 {
     PyObject *result;
     PicklerObject *pickler = _Pickler_New();