PEP8 is your definitive guide for style questions:
and this is an interesting set of notes:
Basic rule is to break within parenthesis -- after that it becomes a matter of personal taste/style.
In your specific example, I would do something like:
"Item wrote to MongoDB database %s %s" % (
Though you might want to:
a) start your string right after the log.msg(
b) put more than one settings on the same line
c) put the last two parameters on the same line.
I find that once I start breaking up lines for length, that I prefer to break up everything.
Also remember when entering long lines of text that strings concatenate within parenthesis.
("a, b, c"
"d, e, f"
"g, h, i")
Is the same as ("a, b, cd, e, fg, h, i")