import math


def euclidean_distance(a, b=None):
    """
    Euclidean distance between two n-dimensional points.
    """
    if b is None: return euclidean_distance(a, (0,) * len(a))
    return math.sqrt(sum((a - b) ** 2 for a, b in zip(a, b)))
    #np.linalg.norm(a - b)
    #np.sqrt(np.sum((a-b)**2)))