Python, calling methods on different objects give the same result

Question

I'm making my first step in object-oriented programming in python and I'm facing a problem that I don't understand.

I've a class "Annotation". Which represents an image of width 'w' and height 'h'.

class Annotation:

    def __init__(self, data, width, height, point_coordinates=[]):
        self.data = data
        self.width = width
        self.height = height
        self.point_coordinates = point_coordinates
        self.nb_point = len(point_coordinates)

I can add points at given coordinates (x,y) on my annotation thanks to the method 'add_point':

def add_point(self, x, y):
    self.point_coordinates.append([x, y])
    self.nb_point += 1

The problem is, in my main function I create 2 annotation objects of different sizes and I add a point to each of my annotations. After that I print the number of points of each of my objects, the result is 1 which is normal. But when I print the list of points of each of my objects the result is the same list...

if __name__ == '__main__':
    ann = Annotation(np.full((512, 512), 127), 512, 512)
    ann2 = Annotation(np.full((120, 120), 1), 120, 120)

    ann.add_point(10, 20) #Add point to annotation 1
    ann2.add_point(1, 1) #Add point to annotation 2

    print("Number of point of ann: ",ann.get_nb_point())    #print (1)
    print("Number of point of ann2: ", ann2.get_nb_point()) #print (1)

    print("Point of ann: ", ann.get_point())    #print  [[10, 20], [1, 1]]
    print("Point of ann2: ", ann2.get_point()) #print  [[10, 20], [1, 1]]

I really don't understand the problem here...

There is the full code of my class:

class Annotation:

    def __init__(self, data, width, height, point_coordinates=[]):
        self.data = data
        self.width = width
        self.height = height
        self.point_coordinates = point_coordinates
        self.nb_point = len(point_coordinates)

    def get_point(self):
        return self.point_coordinates

    def get_nb_point(self):
        return self.nb_point

    def add_point(self, x, y):
        self.point_coordinates.append([x, y])
        self.nb_point += 1


if __name__ == '__main__':
    ann = Annotation(np.full((512, 512), 127), 512, 512)
    ann2 = Annotation(np.full((120, 120), 1), 120, 120)
    ann.add_point(10, 20)
    ann2.add_point(1, 1)
    print("Number of point of ann: ",ann.get_nb_point())    #print (1)
    print("Number of point of ann2: ", ann2.get_nb_point()) #print (1)

    print("Point of ann: ", ann.get_point())    #print  [[10, 20], [1, 1]]
    print("Point of ann2: ", ann2.get_point()) #print  [[10, 20], [1, 1]]