Why do I get “TypeError: not all arguments converted during string formatting” trying to format a tuple?

>>> 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.