Generate a Polynomial Features function in Python Without using Sklearn. Please explain your code.

def create_features (X, degree) : ""'"Creates the polynomial features Input: X: n-by-d array. degree: An integer for the degree of the generated polynomial function. Must be equal or greater than 1. Return: A n-by-d array. For example, if an input x is two dimensional and of the form [a, b]; Then, the degree-2 polynomial features are [a, b, a^2, ab, b^2]