Sqlite3, Operationalerror: Unable to Open Database File

Sqlite3, OperationalError: unable to open database file

Primary diagnosis: SQLite is unable to open that file for some reason.

Checking the obvious reasons why, and in approximate order that I recommend checking:

Is the program running on the same machine as you're testing it?
Is it running as you (or at least the same user as you're testing it as)?
Is the disk containing /tmp full? (You're on Unix, so use df /tmp to find out.)
Does the /tmp/cer directory have “odd” permissions? (SQLite needs to be able to create additional files in it in order to handle things like the commit log.)
Is the unit test code still using that database? (Concurrent opens are possible with a modern-enough SQLite and when in the right filesystem — though /tmp is virtually always on the right sort of FS so it's probably not that — but it's still not recommended.)
Is the development code really trying to write to that database, or is something “clever” catching you out and causing it to try to open something else? (I've been caught out by this in my code in the past; don't think it can't happen to you…)
Are you using the same version of the SQLite library in the unit tests and the production code?

If you're not on the same machine, it's quite possible that the production system doesn't have a /tmp/cer directory. Obvious to fix that first. Similarly, if you're on the same machine but running as different users, you're likely to have permissions/ownership problems. Disk space is another serious gotcha, but less likely. I don't think it's the last three, but they're worth checking if the more obvious deployment problems are sorted. If it's none of the above, you've hit an exotic problem and will have to report much more info (it might even be a bug in SQLite, but knowing the developers of it, I believe that to be quite unlikely).

Python Error just on PC startup sqlite3.OperationalError: unable to open database file

Of course this show that the system cannot find the specified file, this are the reason to they can't open the database file. If your program is in DB folder, you can just use
conn = sqlite3.connect('Todos.db') instead. And, the most recommended if is for personal purposes, is that you use the entire path, like conn = sqlite3.connect('X:\MyDB\SQLite\Todos.db'). The output error sqlite3.OperationalError: unable to open database file begins, normally, with these errors below:

System cannot find the file.
System cannot open the file.
System doesn't have the permission to the file (or you don't have).
System doesn't have READ permissions.

If cannot open find the file, move your script or your directory to the place that the file is. It's economize code, is much better than insert the full path, because if you have making the program to someone, is harder to say where the program is, and he/she will, probably, change the code, etc. But if everything is on a same folder, is a lot easy.

If cannot open the file, probably is corrupted; the program cannot read this ext of file or is not a program that he recognize. Or you don't pay the program.

If don't have permission to the file, you need to start the program as ADMINISTRATOR, if it doesn't work, search in the internet how to give permissions to an .(yourext).

For least, READ permissions is right on the file. Some files has an attrib, the "-r", the Read-only file attribute, remove it with an PROMPT (CMD) with admin rights, being in the folder of the file and typing attrib -r -s -h yourfile.ext, it removes the read-only, system and hidden file attributes.

If everything doesn't work, the file is corrupted. Sorry.