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avoid race conditions

You need a better data storage mechanism

Your initial text files and pickle design is fine when only one user is accessing
the data. However, now that more than one person can access the data at any
time, and from anywhere, your design is in need of improvement. Above all,
you need to avoid that race condition.

This is very Listen, bud, it’s not my fault...until
upsetting...I appear someone, somewhere runs the “put_to_store()”
to be missing an update. function without someone, somewhere else running the
“get_from_store()” function, you’ll have to do without that
data update. I’m not a miracle worker...I just do what
I’m told.

[‘Is this the right room
for an argument?’, “No
you haven’t!”, ‘When?’,
“No you didn’t!”, “You
didn’t!”, ‘You did not!’,
‘Ah! (taking out his wallet
and paying) Just the five
minutes.’, ‘You most
certainly did not!’, “Oh
no you didn’t!”, “Oh no
you didn’t!”, “Oh look,
this isn’t an argument!”,
“No it isn’t!”, “It’s
just contradiction!”,
‘It IS!’, ‘You just
contradicted me!’, ‘You
DID!’, ‘You did just
then!’, ‘(exasperated)
Oh, this is futile!!’,
‘Yes it is!’]
Your inconsistent
and upset pickle file Server
Web
Q: Surely you should have thought about this problem long Q: So I’m facing a rewrite of large chunks of my code?
ago and designed this “properly” from the start?
A: Let’s see. You did build your program using the MVC pattern,
A: That’s certainly one way to look at things, and hindsight is and you are using Python, so those two facts should take the sting
always a wonderful thing! However, programs have a tendency out of any potential rewrite, assuming a rewrite is what’s required
to start out small, then grow to provide more features, which can here.
introduce complexity. Recall that the coach’s app started life as a
simple “standalone” text-based program, which was then moved
to the Web to support multiple users. Part of the app was then
redeveloped for use on an Android phone. And yes, if we’d known all
of this ahead of time, we might have been designed it differently.

310 Chapter 9