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

July 18, 2009


      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