The % in Python, on numbers, is modulo:x = 10 y = 3 x % y # 1 x.__mod__(y) # same thing, 1But str uses __mod__ for interpolation:s = 'Hi, %d' s % y # 'Hi, 3' s.__mod__(y) # Same thing, 'Hi, 3'Same operator, same magic method — but totally different.