msgpack unserialising dict key strings to bytes

A default encoding is set when calling dumps or packb

:param str encoding:
 |      Convert unicode to bytes with this encoding. (default: 'utf-8')

but it is not set by default when calling loads or unpackb as seen in:

Help on built-in function unpackb in module msgpack._unpacker:

unpackb(...)
    unpackb(... encoding=None, ... )

Therefore changing the encoding on the deserialisation fixes the issue, for example:

>>> d['key'] = 1234
>>> binary = msgpack.dumps(d)
>>> msgpack.loads(binary, encoding = "utf-8")
{'key': 1234}
>>> msgpack.loads(binary, encoding = "utf-8") == d
True

Using the raw=False flag as such worked for me on your example:

msgpack.unpackb(binary, raw=False)
# or
msgpack.loads(binary, raw=False)

See https://msgpack-python.readthedocs.io/en/latest/api.html#msgpack.Unpacker:

raw (bool) – If true, unpack msgpack raw to Python bytes. Otherwise, unpack to Python str by decoding with UTF-8 encoding (default).