[Python-ideas] Make return inside a finally a SyntaxError

[MRAB]

MRAB wrote:
> Michael wrote:
>> Here are two examples of why allowing return inside a finally block is 
>> a bad idea:
>>
>> def f():
>>   try:
>>     return 3
>>   finally:
>>     return 4
>>
>> def f():
>>   try:
>>     raise Exception()
>>   finally:
>>     return 4
>>
> I wouldn't call that a syntax error. Wouldn't you also have to forbid 
> break, continue and, perhaps, yield?
> 
I shouldn't checked before posting... :-(


Test 1: break swallows the exception.

 >>> for n in range(3):
	try:
		print n
		raise IndexError
	finally:
		break

	
0


Test 2: continue raises a SyntaxError.

 >>> for n in range(2):
	try:
		print n
		raise IndexError
	finally:
		continue
	
SyntaxError: 'continue' not supported inside 'finally' clause


Test 3: yield propagates the exception on resuming.

 >>> def test():
	for n in range(3):
		try:
			print n
			raise IndexError
		finally:
			print "yielding", n
			yield n

			
 >>> t = test()
 >>> t.next()
0
yielding 0
0
 >>> t.next()

Traceback (most recent call last):
   File "<pyshell#24>", line 1, in <module>
     t.next()
   File "<pyshell#21>", line 5, in test
     raise IndexError
IndexError