TypeError when fetching a mapping

[dduong42]

Environment: Python 3

When fetching for a mapping I got this error:

In [1]: import pyes

In [2]: es = pyes.es.ES()

In [3]: data = es.indices.get_mapping(doc_type='category', indices='catalog')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-7fea737910c0> in <module>()
----> 1 data = es.indices.get_mapping(doc_type='category', indices='catalog')

/home/daniel/.envs/oshop/lib/python3.4/site-packages/pyes/managers.py in get_mapping(self, doc_type, indices, raw)
    453         mapper = Mapper(result, is_mapping=False,
    454                         connection=self.conn,
--> 455                         document_object_field=self.conn.document_object_field)
    456         if doc_type:
    457             return mapper.mappings[doc_type]

/home/daniel/.envs/oshop/lib/python3.4/site-packages/pyes/mappings.py in __init__(self, data, connection, is_mapping, document_object_field)
    825         self.full_mappings = False
    826         self.document_object_field = document_object_field
--> 827         self._process(data)
    828 
    829     def _process(self, data):

/home/daniel/.envs/oshop/lib/python3.4/site-packages/pyes/mappings.py in _process(self, data)
    835             idata = []
    836             for docname, docdata in list(indexdata.get("mappings", {}).items()):
--> 837                 o = get_field(docname, docdata, document_object_field=self.document_object_field, is_document=True)
    838                 o.connection = self.connection
    839                 o.index_name = indexname

/home/daniel/.envs/oshop/lib/python3.4/site-packages/pyes/mappings.py in get_field(name, data, default, document_object_field, is_document)
    793         else:
    794             data.pop("name",None)
--> 795             return DocumentObjectField(name=name, **data)
    796 
    797     elif _type == "object":

TypeError: __init__() keywords must be strings

After some investigation, the problem comes from this line, converting the keys of the data dictionary into byte objects:

data = keys_to_string(data)