class CtxMgr: def __enter__(self): print("__enter__") return self def __exit__(self, a, b, c): print("__exit__", repr(a), repr(b)) with CtxMgr() as a: print(isinstance(a, CtxMgr)) try: with CtxMgr() as a: raise ValueError except ValueError: print("ValueError") class CtxMgr2: def __enter__(self): print("__enter__") return self def __exit__(self, a, b, c): print("__exit__", repr(a), repr(b)) return True try: with CtxMgr2() as a: raise ValueError print("No ValueError2") except ValueError: print("ValueError2") # These recursive try-finally tests are attempt to get some interpretation # of last phrase in http://docs.python.org/3.4/library/dis.html#opcode-WITH_CLEANUP # "If the stack represents an exception, and the function call returns a ‘true’ # value, this information is “zapped” and replaced with a single WHY_SILENCED # to prevent END_FINALLY from re-raising the exception. (But non-local gotos # will still be resumed.)" print("===") with CtxMgr2() as a: try: try: raise ValueError print("No ValueError3") finally: print("finally1") finally: print("finally2") print("===") try: try: with CtxMgr2() as a: try: try: raise ValueError print("No ValueError3") finally: print("finally1") finally: print("finally2") finally: print("finally3") finally: print("finally4")