Preserving value of variables between subsequent requests in Python Django

Question

I have a Django application to log the character sequences from an autocomplete interface. Each time a call is made to the server, the parameters are added to a list and when the user submits the query, the list is written to a file.

Since I am not sure how to preserve the list between subsequent calls, I relied on a global variable say query_logger. Now I can preserve the list in the following way:

def log_query(query, completions, submitted=False):
    global query_logger
    if query_logger is None:
        query_logger = list()

    query_logger.append(query, completions, submitted)

    if submitted: 
        query_logger = None

While this hack works for a single client sending requests I don't think this is a stable solution when requests come from multiple clients. My question is two-fold:

What is the order of execution of requests: Do they follow first come first serve (especially if the requests are asynchronous)?
What is a better approach for doing this?

It also will not work if you are deploying with a multi process web server. — Graham Dumpleton
– Graham Dumpleton, Commented Jun 12, 2018 at 5:50

Daniel Roseman · Accepted Answer · 2018-06-12 09:11:37Z

2

You must not use global variables for this.

The proper answer is to use the session - that is exactly what it is for.

answered Jun 12, 2018 at 9:11

Daniel Roseman

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1 Comment

Unni Over a year ago

Thanks. That's what I was thinking. Still, had to confirm there are no alternatives.

Jonas · Accepted Answer · 2018-06-12 06:47:43Z

1

If your django server is single-threaded, then yes, it will respond to requests as it receives them. If you're using wsgi or another proxy, that becomes more complicated. Regardless, I think you'll want to use a db to store the information.
I encountered a similar problem and ended up using sqlite to store the data temporarily, because that's super simple and easy to manage. You'll want to use IP addresses or create a unique ID passed as a url parameter in order to identify clients on subsequent requests.

I also scheduled a daily task (using cron on ubuntu) that goes through and removes any incomplete requests that haven't been completed (excluding those started in the last hour).

edited Jun 12, 2018 at 6:47

answered Jun 12, 2018 at 6:06

Jonas

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1 Comment

Unni Over a year ago

Thanks! I think I will go with session as @daniel roseman suggested.

Jerome Anthony · Accepted Answer · 2018-06-12 05:50:38Z

-1

Simplest (bad) solution would be to have a global variable. Which means you need some in memory location or a db to store this info

answered Jun 12, 2018 at 5:50

Jerome Anthony

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2 Comments

Unni Over a year ago

My solution above uses global variables. DB is a possible way to go!

Jerome Anthony Over a year ago

Move the initial assignment outside the scope of the function and test please. Also you might be able to use request.session

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