This function is helpful when you need to provide a callback to a Python
library which may invoke the callback on a background thread. As R functions
must run on the main thread, wrapping the R function with py_main_thread_func()
will ensure that R code is only executed on the main thread.
py_main_thread_func(f)
A Python function that delegates to the passed R function, which is guaranteed to always be called on the main thread.
An R function with arbitrary arguments