# switch stream category,
        # load data,
        # update treeview content
        def load(self, category, force=False):
        
            # get data from cache or download
            if (force or not category in self.streams):
                __print__(dbg.PROC, "load", "update_streams")
                new_streams = self.update_streams(category)
      
                if new_streams:
                
                    # modify
                    [self.postprocess(row) for row in new_streams]

                    # check and modify entry;
                    # assert that title and url are present
                    modified = []
                    for row in new_streams:
                        if None in [row.get("title"), row.get("url")]:
                            next
                        try:
                            modified.append( self.postprocess(row) )
                        except Exception as e:
                            __print__(e, dbg.ERR, row)
                    new_streams = modified
      
                    # don't lose forgotten streams
                    if conf.retain_deleted:
                       self.streams[category] = new_streams + self.deleted_streams(new_streams, self.streams.get(category,[]))
                    else:
                       self.streams[category] = new_streams
      

                if ("url" in row and (row.get("url") not in new)):
                    row["deleted"] = 1
                    diff.append(row)
            return diff

        
        # prepare data for display
        #
        #  - favourite icon
        #  - or deleted icon
        #
        def prepare(self, streams):
            __print__(dbg.PROC, "prepare", streams)

            for i,row in enumerate(streams):
                                            # oh my, at least it's working
                                            # at start the bookmarks module isn't fully registered at instantiation in parent.channels{} - might want to do that step by step rather
                                            # then display() is called too early to take effect - load() & co should actually be postponed to when a notebook tab gets selected first
                                            # => might be fixed now, 1.9.8
                # state icon: bookmark star
                if (conf.show_bookmarks and "bookmarks" in self.parent.channels and self.parent.bookmarks.is_in(streams[i].get("url", "file:///tmp/none"))):

                    # check for availability of PNG file, inject local icons/ filename
                    if homepage_url and favicon.available(homepage_url):
                        streams[i]["favicon"] = favicon.file(homepage_url)
                
            return streams

    
        # data preparations directly after reload        
        # data preparations directly after reload
        #
        # - drop shoutcast homepage links
        # - or find homepage name in title
        #
        def postprocess(self, row):

            # remove non-homepages from shoutcast
            if row.get("homepage") and row["homepage"].find("//yp.shoutcast.")>0:
                row["homepage"] = ""
                
            # deduce homepage URLs from title