Incompatibility with pypy interpreter

Start by running test/test_jsonobjects.py with PyPy and inspect the failing import in src/jsonconversion/encoder.py, with test/testing_utils.py showing how the encoder is used. The work is done when the tests run under PyPy without relying on the unavailable json.encoder member.

When trying to use jsonconversion with the pypy interpreter (e.g. pypy3.6 /custom/patch/python-jsonconversion/test/test_jsonobjects.py) the following error occurs:

  File "/home/basti/develop/python-jsonconversion/test/test_jsonobjects.py", line 12, in <module>
    from testing_utils import convert_with_assertion
  File "/home/basti/develop/python-jsonconversion/test/testing_utils.py", line 17, in <module>
    from jsonconversion.encoder import JSONObjectEncoder
  File "/home/basti/develop/python-jsonconversion/src/jsonconversion/encoder.py", line 13, in <module>
    from json.encoder import JSONEncoder, _make_iterencode, encode_basestring, encode_basestring_ascii, INFINITY
ImportError: cannot import name '_make_iterencode'

The '_make_iterencode' is a protected member os json.encoder. Is there a possibility to only use the public API of json.encoder?