Tail recursion

• A technique/trick to avoid an increasing callstack
• With tail recursion, the calling function frees itself from memory (from the callstack) before recursively calling itself
• With tail recursion, there is no back propagation, because the function is not returned to be calling function but returned directly
• A requisite for tail recursion is that the recursion is the very last statement of the function
• When that is not the case, the function has to be refactored in order to satisfy this requirement, usually by using an accumulator

def factorial_recursive_with_accumulator(n, acc=1):
    if n == 0:
        return acc
    return factorial_recursive_with_accumulator(n - 1, acc * n)