python - 我应该合并内存 (.py) 中的图像还是 View (HTML) 中的图像？

Question

我的facebook app让用户上传图像，选择图像是什么(眼睛、 Nose 、嘴巴或其他 body 部位)，然后可以通过按类别选择三个随机图像来组合，这样效果很好，代码看起来不错且可读，但不是很高级:

class CyberFazeHandler(BaseHandler):

    def get_random_image(self, category):
        fileinfos = FileInfo.all().filter("category =", category)
        return fileinfos[random.randint(0, fileinfos.count()-1)] 

    def get(self):
        eyes_image = self.get_random_image(category="eyes")
    nose_image = self.get_random_image(category="nose")
    mouth_image = self.get_random_image(category="mouth")
        eyes_data = None
        try:
        eyes_data = blobstore.fetch_data(eyes_image.blob.key(), 0, 50000)
        except Exception, e:
            self.set_message(type=u'error',
                content=u'Could not find eyes data for file '+str(eyes_image.key().id())+' (' + unicode(e) + u')')

        eyes_img = None

        try:
            eyes_img = images.Image(image_data=eyes_data)

...现在我只获取 3 个随机图像，然后在模板中组合:

<a href="/file/{{eyes_image.key.id}}"><img src="{{eyes_url}}"></a><br>
<a href="/file/{{nose_image.key.id}}"><img src="{{nose_url}}"></a><br>
<a href="/file/{{mouth_image.key.id}}"><img src="{{mouth_url}}"></a>

是否可以通过发送将三幅图像合并为一幅的合成图像来改进这一点？优点是图像上的所有内容都将同时加载，并且如果下次结果已保存时出现随机化，则图像将已保存。你觉得怎么样？

谢谢(应用程序是apps.facebook.com/cyberfaze，您可以检查我这样做是为了娱乐和学习)

全类同学

class CyberFazeHandler(BaseHandler):

    def get_random_image(self, category):
        fileinfos = FileInfo.all().filter("category =", category)
        return fileinfos[random.randint(0, fileinfos.count()-1)] #optimize

    def get(self):
        eyes_image = self.get_random_image(category="eyes")
    nose_image = self.get_random_image(category="nose")
    mouth_image = self.get_random_image(category="mouth")
        eyes_data = None
        try:
        eyes_data = blobstore.fetch_data(eyes_image.blob.key(), 0, 50000)
        except Exception, e:
            self.set_message(type=u'error',
                content=u'Could not find eyes data for file '+str(eyes_image.key().id())+' (' + unicode(e) + u')')

        eyes_img = None

        try:
            eyes_img = images.Image(image_data=eyes_data)
        except Exception, e:
            self.set_message(type=u'error',
                content=u'Could not find eyes img for file '+str(eyes_image.key().id())+' (' + unicode(e) + u')')


        nose_data = None
        try:
            nose_data = blobstore.fetch_data(nose_image.blob.key(), 0, 50000)
        except Exception, e:
            self.set_message(type=u'error',
                content=u'Could not find nose data for file '+str(nose_image.key().id())+' (' + unicode(e) + u')')


        nose_img = None

        try:
            nose_img = images.Image(image_data=nose_data)
        except Exception, e:
            self.set_message(type=u'error',
                content=u'Could not find nose img for file '+str(nose_image.key().id())+' (' + unicode(e) + u')')


        mouth_data = None
        try:
        mouth_data = blobstore.fetch_data(mouth_image.blob.key(), 0, 50000)
        except Exception, e:
            self.set_message(type=u'error',
                content=u'Could not find mouth data for file '+str(eyes_image.key().id())+' (' + unicode(e) + u')')


        mouth_img = None

        try:
            mouth_img = images.Image(image_data=mouth_data)
        except Exception, e:
            self.set_message(type=u'error',
                content=u'Could not find mouth img for file '+str(mouth_image.key().id())+' (' + unicode(e) + u')')


    minimum = min(int(eyes_img.width), int(nose_img.width), int(mouth_img.width))

    eyes_url = images.get_serving_url(str(eyes_image.blob.key()), size=minimum)
    nose_url = images.get_serving_url(str(nose_image.blob.key()), size=minimum)
    mouth_url = images.get_serving_url(str(mouth_image.blob.key()), size=minimum)

        self.render(u'cyberfaze', minimum=minimum, eyes_image=eyes_image, eyes_url=eyes_url, nose_image=nose_image, nose_url=nose_url, mouth_image=mouth_image, mouth_url=mouth_url, form_url = blobstore.create_upload_url('/upload'),)

重写后，它的工作方式如下:

class CyberFazeHandler(BaseHandler):

    def get_random_image(self, category):

        q = FileInfo.all()
        q.filter('category =', category)
        q.filter('randomvalue >=', random.random())
        return q.get()

    def get_random_image_legacy(self, category):
        fileinfos = FileInfo.all().filter('category =', category)
        return fileinfos[random.randint(0, fileinfos.count() - 1)]

    def get(self):

        eyes_image = self.get_random_image(category='eyes')
    if not eyes_image:
       logging.debug("getting eyes failed, trying legacy method")
           eyes_image = self.get_random_image_legacy(category='eyes')
        nose_image = self.get_random_image(category='nose')
    if not nose_image:
           nose_image = self.get_random_image_legacy(category='nose')

        mouth_image = self.get_random_image(category='mouth')
    if not mouth_image:
           mouth_image = self.get_random_image_legacy(category='mouth')

        eyes_data = None
        try:
            eyes_data = blobstore.fetch_data(eyes_image.blob.key(), 0,
                    50000)
        except Exception, e:
            self.set_message(type=u'error',
                             content=u'Could not find eyes data for file '
                              + str(eyes_image.key().id()) + ' ('
                             + unicode(e) + u')')

        eyes_img = None

        try:
            eyes_img = images.Image(image_data=eyes_data)
        except Exception, e:
            self.set_message(type=u'error',
                             content=u'Could not find eyes img for file '
                              + str(eyes_image.key().id()) + ' ('
                             + unicode(e) + u')')

        nose_data = None
        try:
            nose_data = blobstore.fetch_data(nose_image.blob.key(), 0,
                    50000)
        except Exception, e:
            self.set_message(type=u'error',
                             content=u'Could not find nose data for file '
                              + str(nose_image.key().id()) + ' ('
                             + unicode(e) + u')')

        nose_img = None

        try:
            nose_img = images.Image(image_data=nose_data)
        except Exception, e:
            self.set_message(type=u'error',
                             content=u'Could not find nose img for file '
                              + str(nose_image.key().id()) + ' ('
                             + unicode(e) + u')')

        mouth_data = None
        try:
            mouth_data = blobstore.fetch_data(mouth_image.blob.key(),
                    0, 50000)
        except Exception, e:
            self.set_message(type=u'error',
                             content=u'Could not find mouth data for file '
                              + str(eyes_image.key().id()) + ' ('
                             + unicode(e) + u')')

        mouth_img = None

        try:
            mouth_img = images.Image(image_data=mouth_data)
        except Exception, e:
            self.set_message(type=u'error',
                             content=u'Could not find mouth img for file '
                              + str(mouth_image.key().id()) + ' ('
                             + unicode(e) + u')')

        minimum = min(int(eyes_img.width), int(nose_img.width),
                      int(mouth_img.width))

        eyes_url = images.get_serving_url(str(eyes_image.blob.key()),
                size=minimum)
        nose_url = images.get_serving_url(str(nose_image.blob.key()),
                size=minimum)
        mouth_url = images.get_serving_url(str(mouth_image.blob.key()),
                size=minimum)

        self.render(
            u'cyberfaze',
            minimum=minimum,
            eyes_image=eyes_image,
            eyes_url=eyes_url,
            nose_image=nose_image,
            nose_url=nose_url,
            mouth_image=mouth_image,
            mouth_url=mouth_url,
            form_url=blobstore.create_upload_url('/upload'),
            )

Answer 1

哪个更有效取决于它的使用方式。如果用户将加载大量此类混搭，则将它们作为单独的图像发送更有意义，因为浏览器缓存的图像会更少(a+b+c 图像而不是 a*b*c)。

但是，您的代码存在更严重的性能问题:

def get_random_image(self, category):
    fileinfos = FileInfo.all().filter("category =", category)
    return fileinfos[random.randint(0, fileinfos.count()-1)] 

每次调用此函数时，它都会执行一次计数操作，其时间复杂度为 FileInfo 实体的数量，然后执行一次偏移查询，其时间复杂度为 O(n)偏移量。这是极其缓慢且低效的，并且随着图像数量的增加，这种情况会变得更加严重。

如果您希望图像集很小(少于几千)并且相当恒定，只需将它们存储在代码中，这将比任何其他选项更快。如果集合较大，或在运行时发生更改，请为每个实体分配一个 0 到 1 之间的随机值，并使用如下查询来检索随机选择的实体:

q = FileInfo.all()
q.filter('category =', category)
q.filter('random >=', random.random())
return q.get()