App Engine: debug and run differ (mystery) - python-2.7

Question

I'm building a wiki and faced a problem when the result during debugging seems to differ from that during the program run.
class WikiPage(Handler):
def get(self, id):
id, existing_article, article_content = self.get_stripped_id_article_content(id)
logging.error(("GET! id: {0}; article: {1}; content: {2}").format(id, existing_article, article_content))
<...>
def strip_id(self, id):
id = id.replace("/", "")
return id
def get_stripped_id_article_content(self, id):
id = self.strip_id(id)
q = Article.all()
q.filter("id = ", id)
existing_article = q.get()
content = existing_article.content if existing_article else ""
return id, existing_article, content
<...>
class CreateEditPage(WikiPage):
def post(self, id):
id, existing_article, article_content = self.get_stripped_id_article_content(id)
user = self.get_user(self.request)
input_content = self.request.get("content")
if existing_article:
existing_article.content = input_content
existing_article.put()
else:
new_article = Article(id = id, content = input_content)
new_article.put()
id, existing_article, article_content = self.get_stripped_id_article_content(id)
logging.error(("POST! In Else. id: {0}; article: {1}; content: {2}").format(id, existing_article, article_content))
id, existing_article, article_content = self.get_stripped_id_article_content(id)
logging.error(("POST! Outside Else. id: {0}; article: {1}; content: {2}").format(id, existing_article, article_content))
self.redirect("/" + str(id))
PAGE_RE = r'(/(?:[a-zA-Z0-9_-]+/?)*)'
app = webapp2.WSGIApplication([('/_edit' + PAGE_RE, CreateEditPage),
(PAGE_RE, WikiPage),
],
debug=True)
First of all, I clear all the content from the database and fluch the memcache.
I run my application:
INFO 2015-10-14 21:06:52,744 sdk_update_checker.py:229] Checking for updates to the SDK.
INFO 2015-10-14 21:06:53,135 api_server.py:205] Starting API server at: http://localhost:53588
INFO 2015-10-14 21:06:53,141 dispatcher.py:197] Starting module "default" running at: http://localhost:8080
INFO 2015-10-14 21:06:53,142 admin_server.py:118] Starting admin server at: http://localhost:8000
ERROR 2015-10-14 21:10:10,804 gmv_wiki.py:194] GET! id: ; article: None; content:
INFO 2015-10-14 21:10:10,810 module.py:809] default: "GET / HTTP/1.1" 302 -
INFO 2015-10-14 21:10:10,847 module.py:809] default: "GET /_edit/ HTTP/1.1" 200 348
ERROR 2015-10-14 21:10:12,228 gmv_wiki.py:194] GET! id: newpost; article: None; content:
INFO 2015-10-14 21:10:12,239 module.py:809] default: "GET /newpost HTTP/1.1" 302 -
INFO 2015-10-14 21:10:12,264 module.py:809] default: "GET /_edit/newpost HTTP/1.1" 200 348
ERROR 2015-10-14 21:10:18,945 gmv_wiki.py:194] GET! id: new_article; article: None; content:
INFO 2015-10-14 21:10:18,951 module.py:809] default: "GET /new_article HTTP/1.1" 302 -
INFO 2015-10-14 21:10:18,976 module.py:809] default: "GET /_edit/new_article HTTP/1.1" 200 348
ERROR 2015-10-14 21:10:50,979 gmv_wiki.py:246] POST! In Else. id: new_article; article: None; content:
ERROR 2015-10-14 21:10:50,985 gmv_wiki.py:251] POST! Outside Else. id: new_article; article: None; content:
INFO 2015-10-14 21:10:50,991 module.py:809] default: "POST /_edit/new_article HTTP/1.1" 302 -
ERROR 2015-10-14 21:10:51,014 gmv_wiki.py:194] GET! id: new_article; article: None; content:
INFO 2015-10-14 21:10:51,022 module.py:809] default: "GET /new_article HTTP/1.1" 302 -
INFO 2015-10-14 21:10:51,051 module.py:809] default: "GET /_edit/new_article HTTP/1.1" 200 348
ERROR 2015-10-14 21:11:18,321 gmv_wiki.py:251] POST! Outside Else. id: new_article; article: <gmv_wiki.Article object at 0x7f684d2ba250>; content: New article content.
INFO 2015-10-14 21:11:18,326 module.py:809] default: "POST /_edit/new_article HTTP/1.1" 302 -
ERROR 2015-10-14 21:11:18,351 gmv_wiki.py:194] GET! id: new_article; article: <gmv_wiki.Article object at 0x7f684d2663d0>; content: New article content.
INFO 2015-10-14 21:11:18,358 module.py:809] default: "GET /new_article HTTP/1.1" 200 262
I debug my application:
pydev debugger: starting (pid: 10230)
INFO 2015-10-14 21:12:24,730 sdk_update_checker.py:229] Checking for updates to the SDK.
INFO 2015-10-14 21:12:25,435 api_server.py:205] Starting API server at: http://localhost:44302
INFO 2015-10-14 21:12:25,463 dispatcher.py:197] Starting module "default" running at: http://localhost:8080
INFO 2015-10-14 21:12:25,467 admin_server.py:118] Starting admin server at: http://localhost:8000
pydev debugger: starting (pid: 10250)
ERROR 2015-10-14 21:12:36,523 gmv_wiki.py:194] GET! id: new_article_1; article: None; content:
INFO 2015-10-14 21:12:36,547 module.py:809] default: "GET /new_article_1 HTTP/1.1" 302 -
INFO 2015-10-14 21:12:36,766 module.py:809] default: "GET /_edit/new_article_1 HTTP/1.1" 200 348
ERROR 2015-10-14 21:12:54,394 gmv_wiki.py:246] POST! In Else. id: new_article_1; article: None; content:
ERROR 2015-10-14 21:12:54,430 gmv_wiki.py:251] POST! Outside Else. id: new_article_1; article: None; content:
INFO 2015-10-14 21:12:54,452 module.py:809] default: "POST /_edit/new_article_1 HTTP/1.1" 302 -
ERROR 2015-10-14 21:12:54,587 gmv_wiki.py:194] GET! id: new_article_1; article: <gmv_wiki.Article object at 0x7fad181bef10>; content: New article 1 content.
INFO 2015-10-14 21:12:54,610 module.py:809] default: "GET /new_article_1 HTTP/1.1" 200 266
Could you have a look at cases of logging.error in the code. And the results in the log.
Two absolutely equal situations.
http://localhost:8080/new_article # ordinary run
http://localhost:8080/new_article_1 # debug
The behaviour of the program is as follows:
1. During debugging everything works well: edit form for a new article is created and when I press "Submit", the content is placed to the database and I'm redirected to the wiki page of that article.
2. When I just run the program (not debug it), edit form for a new article opens, I input something and press "Submit". Then I'm redirected to the wiki page. No wiki page is found at that address. I'm redirected again to the edit page. And then when I again input the content, the content is finally put into the database and the wiki page opens.
Mysteries for me are:
1. Why there is a difference between running and debugging?
2. Why after I have done new_article.put(), I still have no article object found in the post function?
3. Then I'm redirected to the wiki page, and somehow article object is found. Strange.
4. Why existing_article.put() works well whereas new_article.put() don't place anything to the database?
Well, I seem to be at my wits end. Could you be so kind as to help me with these problems. Thank you in advice.

Answer 1

I suspect you're running into GAE datastore eventual consistency issues. Basically a new article saved in new_article.put() won't be found in the Article.all() query for a (typically short) while. You can still access it by id, tho, but you'd have to adjust your code for that.
I suspect the difference in behaviour is caused by the lower overall speed of debug-mode execution which can hide the eventual consistency issues.