How does a mesh become normal?

Question

I found a pre-written function that seems to normalize the vertices of the mesh, but I can not figure out what v1, v2, f_n, and f_ y are?

def readFaceInfo(obj_path):
vert_list = np.zeros((1,3), dtype='float32')  
face_pts = np.zeros((1,3,3), dtype='float32')
face_axis = np.zeros((1,3,3), dtype='float32')
with open(obj_path, 'r') as f:
    while(True):
        line = f.readline()
        if not line:
            break
        if line[0:2] == 'v ':
            t = line.split('v')[1] # ' 0.1 0.2 0.3'
            vertex = np.fromstring(t, sep=' ').reshape((1,3))
            vert_list = np.append(vert_list, vertex, axis=0)
        elif line[0:2] == 'f ':
            t = line.split() # ['f', '1//2', '1/2/3', '1']
            p1,p2,p3 = [int(t[i].split('/')[0]) for i in range(1,4)]

            points = np.array([vert_list[p1], vert_list[p2], vert_list[p3]])
            face_pts = np.append(face_pts, points.reshape(1,3,3), axis=0)

            ###!!!!!!!!!!!!###
            v1 = vert_list[p2] - vert_list[p1]  # x axis
            v2 = vert_list[p3] - vert_list[p1]
            f_n = np.cross(v1, v2)      # z axis, face normal
            f_y = np.cross(v1, f_n)     # y axis
            new_axis = np.array([unit(v1), unit(f_y), unit(f_n)])
            face_axis = np.append(face_axis, new_axis.reshape((1,3,3)), axis=0)

face_pts = np.delete(face_pts, 0, 0)
face_axis = np.delete(face_axis, 0, 0)
return face_pts, face_axis

I checked the range of vertices and they are all between 0.5 and -0.5. However, does the difference between two vertices in 3D space normalize vertices?