clarified pickle version requirements (fixes #186)
diff --git a/docs/advanced.rst b/docs/advanced.rst
index 9659709..9195d57 100644
--- a/docs/advanced.rst
+++ b/docs/advanced.rst
@@ -1340,13 +1340,15 @@
p = Pickleable("test_value")
p.setExtra(15)
- data = pickle.dumps(p, -1)
+ data = pickle.dumps(p, 2)
-Note that only the cPickle module is supported on Python 2.7. It is also
-important to request usage of the highest protocol version using the ``-1``
-argument to ``dumps``. Failure to follow these two steps will lead to important
-pybind11 memory allocation routines to be skipped during unpickling, which will
-likely cause memory corruption and/or segmentation faults.
+Note that only the cPickle module is supported on Python 2.7. The second
+argument to ``dumps`` is also crucial: it selects the pickle protocol version
+2, since the older version 1 is not supported. Newer versions are also fine—for
+instance, specify ``-1`` to always use the latest available version. Beware:
+failure to follow these instructions will cause important pybind11 memory
+allocation routines to be skipped during unpickling, which will likely lead to
+memory corruption and/or segmentation faults.
.. seealso::
diff --git a/example/example15.py b/example/example15.py
index 9868b62..1810d3e 100644
--- a/example/example15.py
+++ b/example/example15.py
@@ -14,7 +14,7 @@
p.setExtra1(15)
p.setExtra2(48)
-data = pickle.dumps(p, -1) # -1 is important (use highest protocol version)
+data = pickle.dumps(p, 2) # Must use pickle protocol >= 2
print("%s %i %i" % (p.value(), p.extra1(), p.extra2()))
p2 = pickle.loads(data)