This looks more like a general question than a bug report. You should
probably ask on comp.lang.python or #python@irc.freenode.net.

The "# -*- coding: cp1254 -*-" only specifies the encoding used to save
the source file and it's not related to the encoding used when the data
are printed or sent over the network. This should be the same for both
Py2 and Py3.
The browser determines the encoding reading it from the HTTP headers,
from the content-type in the HTML <meta> tag or from the XML
declaration. If none of these are available it tries to determine it
from the content of the file. You should probably specify the encoding
in the headers and encode the data you send accordingly.

Closing as invalid.