[python] 'TTYOutStream' object has no attribute 'buffer'

**Environment**
Anaconda Python 3.9 Spyder IDE
haxe 4.3.0-rc.a49b191

When I try to run my haxe library on [Anaconda Python](https://www.anaconda.com), I get this error

```
File ~\anaconda3\envs\Economic\lib\site-packages\lightstreamer_client\com_lightstreamer_client.py:1687 in printString
python_lib_Sys.stdout.buffer.write(_hx_str.encode("utf-8", "strict"))

AttributeError: 'TTYOutStream' object has no attribute 'buffer'
```

As far as I understand from the haxe source code, the class python.lib.Sys has an attribute `stdout` of type python.lib.io.TextIOBase, which does have a `buffer` attribute (of type BufferedIOBase).

So why do I get the above error?