Dropped the part that says: "For objects that do not provide sequence protocol".
.. index:: builtin: len
- Returns the number of objects in sequence *o* on success, and ``-1`` on failure.
- For objects that do not provide sequence protocol, this is equivalent to the
- Python expression ``len(o)``.
+ Returns the number of objects in sequence *o* on success, and ``-1`` on
+ failure. This is equivalent to the Python expression ``len(o)``.
.. c:function:: PyObject* PySequence_Concat(PyObject *o1, PyObject *o2)