context manager with

ctx.py

class TraceBlock:
    def message(self, arg):
        print("running" + arg)

    def __enter__(self):
        print("starting with block")
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        if exc_type is None:
            print("exited normally\n")
        else:
            print("raise an exception! " + str(exc_type))
            return False # propogate

if __name__ == "__main__":
    with TraceBlock() as action, TraceBlock() as action2:
        action2.message("test 2")
        action.message("test 1")

starting with block
starting with block
runningtest 2
runningtest 1
exited normally
exited normally