Fix issue for python3.9+

[Clivern]

What does this change?

fromstring method is removed since python 3.9. There was a note in previous versions to switch from fromstring into
frombytes. here is the links

https://docs.python.org/3.8/library/array.html#array.array.frombytes
https://docs.python.org/3.8/library/array.html#array.array.fromstring

How to test

Test it in any py3.9 environment. clearly it is broken

How can we measure success?

N/A

Have we considered potential risks?

frombytes is available since python 3.2 but not older versions. so if someone still uses something older than 3.2, frombytes won't work for him