Resolve sqlite3.OperationalError (replacing shelve with diskcache)

[alensiljak]

With Python 3.13, using bean-price results in

dbm.sqlite3.error: unable to open database file

because shelve does not support multi-threaded access.

diskcache is a better multi-platform and multi-threaded alternative to shelve, for caching.
There is a practical difference, where the current cache file needs to be deleted, if it exists. diskcache is using a directory instead of a filename, and puts the sqlite database in there.

resolves #91

[alensiljak]

One item that needs to be resolved is the discrepancy between the two libraries. shelve accepts a path and creates a file, while diskcache will create a directory with the same name.
In effect, this means, if you already have a cache with the default name, diskcache will fail to create a directory with the same name.
We could add some code that checks if the path exists and it is a file, then deletes it. This would make the transition seamless for existing users.

[alensiljak]

This should now be ready to go, if you agree.

[alensiljak]

I've been using this locally and everything seems to work fine.
Any feedback about the change?

Setting up bean-price on other devices is difficult due to links, hence it would be helpful to have this merged and published as a package at some point.

[bastidest]

This resolves #91 for me.

[Boelensman1]

Any updates on this?