Last version, using unpackb: > unpackb() got an unexpected keyword argument 'max_buffer_size' From the [docs](https://msgpack-python.readthedocs.io/en/stable/api.html): > msgpack.unpackb > See Unpacker for options. The reader follow the docs and goes to read Unpacker ... > max_str_len, max_bin_len : Deprecated, use max_buffer_size instead Yes, max_buffer_size doesn't exist in the unpackb declaration. However, the documentation is confusing. **Solution** unpack should have its own argument description, without referring to another function with a different signature.