Need strict mode - rather than cycling back to index 1

[Johnlon]

I want to be sure that only two calls are made, index 1 and index 2 to an api.
At present if a call it made a third time then the library cycles back to index 1 and serves that file instead.
What I want instead is the ability to cause a "resource file not found" error.

I can bodge what I need by created a file with index 3 and putting some non-json like the string "POISON-PILL" into the file, but that's not very intuitive.

Perhaps this can be achieved by a change to the Python API?

Perhaps a backwards compat approach would be some logic that has a fallback when "Api_3.json" isn't found then it double checks for a file like "Api_3.unexpected" instead and if found then it aborts rather than cycling back to 1.

I realise on ivestigation that if #38 is implemented well then it would probably have exactly the result I want.