python 3.5 - How do I switch to constant movement when holding down a key in pygame? -

the following code set when avatar blitted screen , space bar or key tapped moves once when held down isn't moved (in air). need change code when key held down move constant.

import pygame, sys, time, random pygame.locals import *  class player(duck):     """the player controlled duck"""       def __init__(self, x, y, width, height):         super(player, self).__init__(x, y, width, height)          # how many pixels player duck should move on given frame.         self.y_change = 0         # how many pixels spaceship should move each frame key pressed.         self.y_dist = 50       def movekeydown(self, key):         """responds key-down event , moves accordingly"""          if (key == pygame.k_up or key == k_space):             self.rect.y -= self.y_dist     def movekeyup(self, key):         """responds key-up event , stops movement accordingly"""          if (key == pygame.k_up or key == k_space):             self.rect.y -= self.y_dist       def update(self):         """         moves spaceship while ensuring stays in bounds         """         # moves relative current location.         self.rect.move_ip(self.y_change, 0)          # if spaceship moves off screen, put on.         if self.rect.y <= 0:             self.rect.y = 0         elif self.rect.y > window_width:             self.rect.y = window_width  while true:  # main game loop     event in pygame.event.get(): #closes game         if event.type == quit:             pygame.quit()             sys.exit()         elif event.type == pygame.keyup:             player.movekeyup(event.key)         elif event.type == pygame.keydown:             player.movekeydown(event.key) 

in movekeydown method have set self.y_change value desired speed , not adjust self.rect.y value. self.rect.move_ip call in update method move sprite. have call update method every frame in main while loop.

def __init__(self, x, y, width, height):     super(player, self).__init__(x, y, width, height)     # how many pixels player duck should move on given frame.     self.x_change = 0     self.y_change = 0     # how many pixels spaceship should move each frame key pressed.     self.speed = 50  def movekeydown(self, key):     """responds key-down event , moves accordingly."""     if key in (pygame.k_up, pygame.k_space):         self.y_change = -self.speed  def movekeyup(self, key):     if key in (pygame.k_up, pygame.k_space) , self.y_change < 0:         self.y_change = 0  def update(self):     self.rect.move_ip(self.x_change, self.y_change)