The tomorrow module runs a "Syntax Error" in Python version 3.8.1 due to the name "async". I made a correction by changing the function name to "_async".
Change def async(n, base_type, timeout=None): to
def _async(n, base_type, timeout=None):
And def threads(n, timeout=None):
change return return async(n, ThreadPoolExecutor, timeout) to
return _async(n, ThreadPoolExecutor, timeout)