For me, This error was caused when I was attempting to pass in a tuple into the string format method.
I found the solution from this question/answer
Copying and pasting the correct answer from the link (NOT MY WORK):
>>> thetuple = (1, 2, 3)
>>> print "this is a tuple: %s" % (thetuple,)
this is a tuple: (1, 2, 3)
Making a singleton tuple with the tuple of interest as the only item, i.e. the (thetuple,) part, is the key bit here.