исправил `staticmethod` на обычный метод

message.py

@@ -38,10 +38,10 @@ class Slack(object):
             self.post = Post(post, attachments=True)
     def create_attachments(self):
-        data_to_send = Post.post_data_prepare(self.post)
+        data_to_send = self.post.json_prepare()
         try:
             if self.repost:
-                data_repost_to_send = Post.post_data_prepare(self.repost)
+                data_repost_to_send = self.repost.json_prepare()
                 return json.dumps([data_to_send, data_repost_to_send])
         except AttributeError:
             data_to_send['mrkdwn_in'] = ['text']
@@ -88,18 +88,17 @@ class Post(object):
                 return image_url, thumb_url
             else:
                 return None, None
-    
-    @staticmethod
-    def post_data_prepare(post):
+
+    def json_prepare(self):
         return {
             'fallback':    '',
-            'color':       post.color,
-            'text':        post.text,
-            'ts':          post.ts,
-            'footer':      post.footer,
-            'footer_icon': post.footer_icon,
-            'image_url':   post.image_url,
-            'thumb_url':   post.thumb_url,
+            'color':       self.color,
+            'text':        self.text,
+            'ts':          self.ts,
+            'footer':      self.footer,
+            'footer_icon': self.footer_icon,
+            'image_url':   self.image_url,
+            'thumb_url':   self.thumb_url,
         }