Thanks again JonB,
It crashes first time, anytime, totally random.
There are no globals, no matplotlib, no objc_util, no ImageView, no asyncio, no threading, no webview. I use webbrowser.
I can understand that memory may need to be released but it can crash before any webbrowser call.
Just now Pythonista crashed out to iOS after I stopped execution and while I was thumbing through the results on the console i.e. not a script problem. This seems to answer my question that Pythonista is inherently unstable.
I am also encountering slow execution on my <1MB data txt file so MacBook could be a good investment and I have to take pot luck again in choosing a python interpreter. iCloud seeks also seem slow but that's unavoidable.
But on researching I find the old MacBook range does not offer much faster execution and can be slower at times. Macbook M1 is faster but not by anywhere near as much as Apple is claiming and some apps need reinterpretation by Rosetta which slows it enormously.
All this makes me wonder if re-installing pythonista would help and would it find my old files automatically