A thorough testing will be required, as version 0.20 breaks some things. While
doing a quick testing, one issue was found so far.

Issue with strings

The Debug() function needs to accept both unicode and bytes strings. In version 0.19.2 of Cython you could pass unicode string and it was converted automatically, but with the new version an error is throwed:

 TypeError: Expected str, got unicode

The Debug() function:
https://code.google.com/p/cefpython/source/browse/cefpython/utils.pyx?r=2f6f611c2fcf#20

Called from CreateJavascriptCallback():
https://code.google.com/p/cefpython/source/browse/cefpython/javascript_callback_cef3.pyx?r=2f6f611c2fcf

The functionName param was decoded from the cefpython IPC message using the json library, and the json library automatically converted the string to unicode.

There might be more places where unicode is passed and it would throw an error.