This function needed to return an int array. One way to do this was to build a new array and add the min and max to it and then return. But here you are doing it in one step without giving the array a variable name. You create a new int[] and initialize it all in one line.

Be a good scout, improve code before leaving.

str(digits[x]*2) - gives you a string, it consist of one or two characters

map( int, str(digits[x]*2) ) - transform your string to an int array

sum ( ---- ) takes sum of the elements, if the multiplication result is single digit then sum of array's elements equal to the element value. if the multiplication result is two digits then it takes sum of it, like should be described by the algorithm

How does this approach handle when the resulting "digit" after multiplying by 2 is greater than 9?

I also don't think this solution solves the Kata as written. This changes the class in order to make push a one line function. Since the original class declaration didn't have an argument for next I feel this misses the point.