The program below triggers a UnicodeEncodeError on my Windows 10 machine (running Python 3.5.2) but no error at all on my Linux machine (running Python 3.3.2).
str ="Antonín Dvořák"
Instead of a file name, you could pass a stream whose encoding is specified:
logging.basicConfig( stream=open('log.txt', 'w', encoding='utf-8'), level=logging.INFO )
As for the cause, it's probably trying to open the target file using your current locale's encoding (CP1252, judging by the stack trace).