[bug]: exchange_rate: it does not work for GBP to USD

[mcgizzle]

Check the bug has not already been reported

• I could not find the bug in existing issues

Edit function_name and the short error description in title above

• I wrote the correct function name and a short error description in the title above

What happened and what did you expect?

select bigfunctions.eu.exchange_rate('GBP', 'USD') returns null

It works in all other cases I tested, even the reverse exchange_rate('USD', 'GBP') works

[unytics]

Thanks a lot @mcgizzle for opening this issue.

I suspect this happens when there are too many calls to yahoo finance.

I improved the function by:

• checking the country given in input against ISO 4217 country codes and do NOT calling yahoo finance if the country code is not valid.
• improving the cache management by NOT storing None in cache if yfinance does not return expected result.

I hope it will solve the issue.

Can you please tell me if you encounter null values again?

Thanks