Common sequence comparison in Python

Very simple program which should be done in Python. Program should take two arrays of tokens as input. It should then find all the common sequences of both arrays (minimum size of a substring is 3, but this variable should be able to be changed). And then perform the following calculation: (number of common substrings of both arrays) / (total substrings of in array1 + total substrings of in array2). The program should then prints the result of the calculation to terminal.