PyGame Physics UPDATED!

#pygame Test by KNovak
import pygame, sys, os, math
from pygame.locals import *
pygame.init()
pygame.key.set_repeat(1)
fullscreen = False;

#startup settings
for arg in sys.argv:
    if arg == "-f":
        fullscreen = True


#Video Display information
vidinfo = pygame.display.Info()

if fullscreen == True:
    vidsize = (vidinfo.current_w, vidinfo.current_h)
    window = pygame.display.set_mode(vidsize, pygame.FULLSCREEN)
else:
    vidsize = (640,480)
    window = pygame.display.set_mode(vidsize)
pygame.display.set_caption('KNova Test Window')
screen = pygame.display.get_surface()
background = pygame.Surface((screen.get_width(), screen.get_height()))

#colors
WHITE = (255,255,255)
BLUE = (0,0,150)
GREEN = (0,150,0)

#text
def drawText (text, color, xloc, yloc, size):
    fontObj = pygame.font.Font('freesansbold.ttf', size)
    textSurface = fontObj.render(text, True, color)
    textRectObj = textSurface.get_rect()
    textRectObj.center = (xloc, yloc)
    return textSurface, textRectObj

####################################################
#Sprite Class for the Ship Image

class Ship(pygame.sprite.Sprite):
    image = pygame.image.load("./resources/ship.png")
    image = image.convert()

    #initialization function
    def __init__(self, position=(100,100)):
        pygame.sprite.Sprite.__init__(self,self.groups)
        self.pos = position
        self.orig_image = Ship.image
        self.image = self.orig_image
        self.rect = self.image.get_rect()
        self.rect.center = self.pos
        self.angle = 0
        self.vx, self.vy, self.speed = 0, 0, 0
        self.maxvel = 4
        self.moving = 0

    #move function
    def move(self, newpos):
        oldx, oldy = self.pos
        dx, dy = newpos
        self.pos = (oldx - dx, oldy - dy)
        self.rect.center = self.pos


    #update function which will replace both move and rotate
    def update(self):

        #handle rotations
        if self.angle >= 360:
            self.angle = 0
        if self.angle <= -360:
            self.angle = 0
        loc = self.rect.center
        self.image = pygame.transform.rotate(self.orig_image, self.angle)
        self.rect = self.image.get_rect()
        self.rect.center = loc

        #handle 2D movement
        if self.moving: self.velocity(self.speed)
        self.move((self.vx, self.vy))


        #boundaries
        if self.pos[0] > vidsize[0]:
            #right
            self.vx = -self.vx
        if self.pos[0] < 0:
            #left
            self.vx = -self.vx
        if self.pos[1] > vidsize[1]:
            #bottom
            self.vy = -self.vy
        if self.pos[1] < 0:
            #top
            self.vy = -self.vy

    #update velocity
    def velocity(self, speed):
        self.vx += math.sin(math.radians(self.angle)) * speed
        self.vy += math.cos(math.radians(self.angle)) * speed

        magnitude = math.sqrt(self.vx*self.vx + self.vy*self.vy)
        if magnitude > self.maxvel:
            self.vx *= 4/magnitude
            self.vy *= 4/magnitude
        if self.speed >= self.maxvel:
            self.speed = self.maxvel
        if self.speed <= -self.maxvel:
            self.speed = -self.maxvel

####################################################

#sprite group update
def spriteUpdate(group, screen, background):
    group.clear(screen, background)
    group.update()
    group.draw(screen)


#get keyboard events
def pyin(events):
    for event in events:
        if event.type == QUIT:
            sys.exit(0)
        if event.type == KEYDOWN:
            key = pygame.key.get_pressed()
            if (key[pygame.K_ESCAPE]):
                sys.exit(0)

            if (key[K_UP]):
                newShip.speed += 1
                newShip.moving = 1

            if (key[K_DOWN]):
                newShip.speed -= 1
                newShip.moving = 1

            if (key[K_LEFT]):
                newShip.angle += 4

            if (key[K_RIGHT]):
                newShip.angle -= 4

        if event.type == KEYUP:
            if event.key == pygame.K_UP:
                newShip.moving = 0
            if event.key == pygame.K_DOWN:
                newShip.moving = 0



spriteGroup = pygame.sprite.Group()
Ship.groups = spriteGroup
newShip = Ship()
clock = pygame.time.Clock()


while True:
    #clock
    clock.tick(60)

    #input detection / handling
    pyin(pygame.event.get())

    #graphics update
    pygame.display.update()
    spriteUpdate(spriteGroup, screen, background)