import sys
import contextlib
import traceback

class AnException(Exception):
	pass

@contextlib.contextmanager
def causes_exception():
	"raise AnException"
	pass
	try:
		raise AnException("yikes")
		yield 1
	finally:
		pass

@contextlib.contextmanager
def what_exception():
	"suffocate AnException"
	pass
	try:
		yield None
	except AnException:
		# what exception? things are just fine.
		pass
	finally:
		pass

@contextlib.contextmanager
def cleanup_or_finish():
	try:
		print "setup, good"
		yield None
	except Exception, e:
		print "cleanup, bad"
		traceback.print_exception(*sys.exc_info())
	else:
		print "finished, no exception seen. good."

print
print "using nested with statements:"
print

with cleanup_or_finish():
	with what_exception():
		with causes_exception():
			print "inner, should never print"

print
print "using nested():"
print

with contextlib.nested(cleanup_or_finish(), what_exception(), causes_exception()):
	print "iieee, should never get here"