Why does this dot product give a dimension error?

Question

This code gives an error stating the important dimension of the rotation matrix and the important dimension of the vector describing the vertex is different. It states that the rotation matrix has dimension (2, 2, 1). This is test code, my full program is bigger but contains another 'Asteroids' function that works fine but this one doesn't. Can someone help?

import pygame
import pygame.locals
import numpy
import random

asteroids = []
amount = 50
screen = (1600, 1200)

pygame.init()
display = pygame.display.set_mode(screen)
clock = pygame.time.Clock()

def rotation(angle):
    rotation = numpy.array([[numpy.cos(angle), -numpy.sin(angle)], [numpy.sin(angle), numpy.cos(angle)]])
    return rotation

def Asteroids(angle):
    offset2 = numpy.array([[-10.0, 0.0], [-8.0, -5.0], [-5.0, -8.0], [0.0, -10.0], [6.0, -8.0], [9.0, -4.0], [4.0, -2.0], [10.0, 0.0], [7.0, 7.5], [2.5, 4.0], [0.0, 10.0], [-6.0, 8.0], [-9.0, 3.0], [-4.0, 0.0]])
    asteroid = []

    for n in range(len(offset2)):
        offset2[n] = rotation(angle).dot(offset2[n])
        asteroid.append(offset2[n])
    return asteroid

def asteroid_creator(amount):
    for i in range(amount):
        i = Boid()
        vec = numpy.random.random_sample(2) - numpy.array([0.5, 0.5])
        i.position = numpy.random.random_sample(2) * screen
        i.velocity = vec / numpy.linalg.norm(vec)
        i.acceleration = numpy.array([0.0, 0.0])
        i.angle = numpy.random.random_sample(1) * 2 * numpy.pi
        asteroids.append(i)

def drawing_asteroid_creator(amount):
    for n in range(amount):
        #pygame.draw.circle(display, (255 - (n / amount * 255), 255 - (n / amount * 255), 255 - (n / amount * 255)), (int(asteroids[n].position[0]), int(asteroids[n].position[1])), 21)
        #pygame.draw.circle(display, (n / amount * 255, n / amount * 255, n / amount * 255), (int(asteroids[n].position[0]), int(asteroids[n].position[1])), 19)
        asteroid_angle = asteroids[n].angle
        vertices = asteroids[n].position + numpy.array([(Asteroids(asteroid_angle)[0]), (Asteroids(asteroid_angle)[1]), (Asteroids(asteroid_angle)[2]), (Asteroids(asteroid_angle)[3]), (Asteroids(asteroid_angle)[4]), (Asteroids(asteroid_angle)[5]), (Asteroids(asteroid_angle)[6]), (Asteroids(asteroid_angle)[7]), (Asteroids(asteroid_angle)[8]), (Asteroids(asteroid_angle)[9]), (Asteroids(asteroid_angle)[10]), (Asteroids(asteroid_angle)[11]), (Asteroids(asteroid_angle)[12]), (Asteroids(asteroid_angle)[13])])
        pygame.draw.polygon(display, (255, 255, 255), (vertices), 2)
        asteroids[n].update()

class Boid:
    def _init_(self):
        self.position = position
        self.velocity = velocity
        self.acceleration = acceleration
        self.angle = angle

    def update(self):
        self.position += self.velocity
        self.velocity += self.acceleration
        self.acceleration = 0

asteroid_creator(amount)

while True:
    display.fill((0, 0, 0))
    drawing_asteroid_creator(amount)

Excuse me, i forgot the error message

Traceback (most recent call last):
  File "c:/Users/Marieke/Documents/Python stuff/Boid2.py", line 176, in <module> 
    drawing_asteroid_creator(amount)
  File "c:/Users/Marieke/Documents/Python stuff/Boid2.py", line 135, in drawing_asteroid_creator
    vertices = asteroids[n].position + numpy.array([(Asteroids(asteroid_angle)[0]), (Asteroids(asteroid_angle)[1]), (Asteroids(asteroid_angle)[2]), (Asteroids(asteroid_angle)[3]), (Asteroids(asteroid_angle)[4]), (Asteroids(asteroid_angle)[5]), (Asteroids(asteroid_angle)[6]), (Asteroids(asteroid_angle)[7]), (Asteroids(asteroid_angle)[8]), (Asteroids(asteroid_angle)[9]), (Asteroids(asteroid_angle)[10]), 
(Asteroids(asteroid_angle)[11]), (Asteroids(asteroid_angle)[12]), (Asteroids(asteroid_angle)[13])])
  File "c:/Users/Marieke/Documents/Python stuff/Boid2.py", line 48, in Asteroids 
    offset2[i] = rotation(angle).dot(offset2[i])
ValueError: shapes (2,2,1) and (2,) not aligned: 1 (dim 2) != 2 (dim 0)
PS C:\Users\Marieke\Documents\Python stuff>

Answer 1

numpy.random.random_sample always returns an array of random values.
So numpy.random.random_sample(1) does not return a single number, it returns an array with 1 element. That causes that rotation creates a 2x2x1 array rather than a 2x2 array.

If you want to generate a single random value, you have to get the first element of the numpy.array which is generated by numpy.random.random_sample :

i.angle = numpy.random.random_sample(1)[0] * 2 * numpy.pi