Develop Reference

Will Flask ever stop detecting changes?

I made a new anaconda installation and happily fired up a Flask program but was promptly overwhelmed. Hundreds and thousands of "detected change in .... reloading". That was three days ago. by yesterday it seemed to have calmed down a bit and would believe it was detecting a change about once every minute. It has kept up that rate since. What I assume is happening is that it is slowly but surely making some kind of map of my python environment.
Does this ever end? Is there anything I can do to speed it up?
Thanks, Tunneller

Try using debug=False in the run statement. For example:
app.run(host='0.0.0.0', debug=False)
This will stop the flask app from detecting changes to files it is using and updating itself.

How do I run Python scripts automatically, while my Flask website is running on a VPS?

Okay, so basically I am creating a website. The data I need to display on this website is delivered twice daily, where I need to read the delivered data from a file and store this new data in the database (instead of the old data).
I have created the python functions to do this. However, I would like to know, what would be the best way to run this script, while my flask application is running? This may be a very simple answer, but I have seen some answers saying to incorporate the script into the website design (however these answers didn't explain how), and others saying to run it separately. The script needs to run automatically throughout the day with no monitoring or input from me.
TIA

Generally it's a really bad idea to put a webserver to handle such tasks, that is the flask application in your case. There are many reasons for it so just to name a few:
Python's Achilles heel - GIL.
Sharing system resources of the application between users and other operations.
Crashes - it happens, it could be unlikely but it does. And if you are not careful, the web application goes down along with it.
So with that in mind I'd advise you to ditch this idea and use crontabs. Basically write a script that does whatever transformations or operations it needs to do and create a cron job at a desired time.

Why is my RPC total going up?

I'm Trying to optimize my code, and I got into a problem I don't quite understand. On every page of my web app, there will be a list of notifications much like Facebook's new ticker. So, on every request, I run this code in the beggining:
notification_query = db.Query(Ticker, keys_only=True)\
.filter('friends =',self.current_user.key().name())
self._notifications_future = notification_query.run()
Then, where I find a good spot, I call the middle function which is:
notification_keys = [future.parent() for future in self._notifications_future]
self._notifications = db.get_async(notification_keys)
Finally I fetch them all at the end:
context.update({'notifications': self._notifications.get_result() })
Every thing works great except for this: If I call the middle function in the end of the request's function, I get this:
Dumb spot
And If I call it in what I think is an optimized spot, I get this:
Smart spot
As you can see the API usage is doubled by making this "optimization". What is going on here?
Call number 2, is the first snippet in both cases. Call number 12 in dumb spot is the second snippet, and call number 12 in the smart spot is the second snippet. This last switch, has nothing to do with the problem, I've tested it.
pd: Does google charge me for time the query is "idle"?
UPDATE
The problem seems to be just in the dev_server, when I tried the same example (smart version) on appspot, I got this:
Queries on appspot
Here everything works as expected, things that get called with run() or get_async() don't block other stuff. As I said the issue is only in dev_server. Still it would be nice to see this feature working on localhost, for more effective profiling.

In addition to Peter's note, you should bear in mind that Appstats has no way to know when an asynchronous request actually completes, except when you fetch the result. As a result, even fast calls will look slow if you take a long time to request the result.

Ahhhh. It is very helpful when posting about app engine to mention if your results are on the dev server or in production. The dev server does not have the same performance characteristics as the production servers, so it is not the best way to profile your application. In fact, I believe that indexes are not used at all, and that the dev server is single threaded, so you can't handle concurrent requests with it. In fact, if your app makes calls to itself, it won't work at all!

How to periodically check for the current date from within a program?

I would like to write a tiny calendar-like application for someone as a birthday present (to be run on Ubuntu). All it should do is display a separate picture each day, so whenever it's invoked it should check the date and select the appropriate picture from the collection I would provide, but also, in case it just keeps running, it should switch to the next picture when the next day begins.
The date-checking on invocation isn't the problem; my question pertains to the second case: how can I have the program notice the beginning of the next day? My clumsy approach would be to make it check the current date at regular intervals and let it change the displayed picture once there was a change in date, but that strikes me as very roundabout and not particularly elegant.
In case any of you have got some idea of how I could accomplish this, please don't hesitate to reply. I would aim to write the application in either Perl or Python, so suggestions concerning those two languages would be most welcome, but any other suggestions would be appreciated as well.
Thanks a lot for your time!

The answer to this could be very system dependant. Controlling the time at which your program is executed is likely to be system dependant. On all *nix type systems, I would use cron. Assuming for a moment that you are using a *nix system, the answer then depends on what the program actually does.
If it only needs to select an image, then I would suggest that it not be run continuously, but terminates itself after selecting it, and is then run again the next day (there are a lot of tutorials on how to setup cron).
If, however, it has some form of UI and it is likely (read possible) to keep running for several days, then you can follow two approaches:
Create your program as it is, to poll periodically for the current time, and do a date delta comparison. Python timedelta objects could help here. This is pretty much your inelegant approach.
The other solution would be to send it a signal from cron when you do wish it to update. This process would mean that you would have to make it signal aware, and respond to something like USR1. The Python docs talk to this, but you can find many tutorials on the web. This approach also works quite nicely for daemonised apps.
I'm sure there are many other approaches too, but those are the ones that come to mind for a quickish and nastyish app.

Did you think about scheduling the invoke of your script?
For me, the best approach is this:
1.Have two options to run the script:
run_script
run_script --update
2.Schedule the update run in some task scheduler (for example Cron) to be executed daily.
3.When you would want to check the image for current day, simply run the script without update option.
If you would like me to extend any part of these, simply ask about it.

Chaining Deferred Tasks with Google App Engine

I have a website I am looking to stay updated with and scrape some content from there every day. I know the site is updated manually at a certain time, and I've set cron schedules to reflect this, but since it is updated manually it could be 10 or even 20 minutes later.
Right now I have a hack-ish cron update every 5 minutes, but I'd like to use the deferred library to do things in a more precise manner. I'm trying to chain deferred tasks so I can check if there was an update and defer that same update a for couple minutes if there was none, and defer again if need be until there is finally an update.
I have some code I thought would work, but it only ever defers once, when instead I need to continue deferring until there is an update:
(I am using Python)
class Ripper(object):
def rip(self):
if siteHasNotBeenUpdated:
deferred.defer(self.rip, _countdown=120)
else:
updateMySite()
This was just a simplified excerpt obviously.
I thought this was simple enough to work, but maybe I've just got it all wrong?

The example you give should work just fine. You need to add logging to determine if deferred.defer is being called when you think it is. More information would help, too: How is siteHasNotBeenUpdated set?