Add isReadOnly property (copied from python2)

I made this simple change to the python3 code, copying from the python2 code.

I was unable to run any of the tests in the github code. Do you have notes for configuration of the share you are using to test?

Sorry about the whitespace changes: my emacs has a presave hook that removes extra whitespace. I think a linter might complain about lines with extra whitespace.