BTree.get(object()) raises TypeError on CPython, returns default on PyPy about btrees HOT 2 CLOSED

Python 2.7.10 (7e8df3df9641, Jun 14 2016, 13:30:54)
[PyPy 5.3.1 with GCC 4.2.1 Compatible Apple LLVM 5.1 (clang-503.0.40)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>> import BTrees
>>>> BTrees.family64.IO.BTree()['a key']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/.tox/pypy/site-packages/BTrees/_base.py", line 1247, in __getitem__
    raise KeyError(key)
KeyError: 'a key'

Python 2.7.12 (default, Jul 11 2016, 16:16:26)
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import BTrees
>>> BTrees.family64.IO.BTree()['a key']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: expected integer key