On 1/30/2014 7:05 AM, Dave Angel wrote:
Jessica Ross <deathwea...@gmail.com> Wrote in message:
I found something like this in a StackOverflow discussion.
def paradox():
... try:
... raise Exception("Exception raised during try")
... except:
... print "Except after try"
... return True
... finally:
... print "Finally"
... return False
... return None
...
return_val = paradox()
Except after try
Finally
return_val
False
I understand most of this.
What I don't understand is why this returns False rather than True. Does the
finally short-circuit the return in the except block?
The finally has to happen before any return inside the try or the
except. And once you're in the finally clause you'll finish it
before resuming the except clause. Since it has a return, that
will happen before the other returns. The one in the except block
will never get reached.
It's the only reasonable behavior., to my mind.
Checking with the disassembled code, it appears that the except return
happens first and is then caught and the value over-written
2 0 SETUP_FINALLY 45 (to 48)
3 SETUP_EXCEPT 16 (to 22)
3 6 LOAD_GLOBAL 0 (Exception)
9 LOAD_CONST 1 ('Exception raised during try')
12 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
15 RAISE_VARARGS 1
18 POP_BLOCK
19 JUMP_FORWARD 22 (to 44)
4 >> 22 POP_TOP
23 POP_TOP
24 POP_TOP
5 25 LOAD_GLOBAL 1 (print)
28 LOAD_CONST 2 ('Except after try')
31 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
34 POP_TOP
6 35 LOAD_CONST 3 (True)
38 RETURN_VALUE
39 POP_EXCEPT
40 JUMP_FORWARD 1 (to 44)
43 END_FINALLY
>> 44 POP_BLOCK
45 LOAD_CONST 0 (None)
8 >> 48 LOAD_GLOBAL 1 (print)
51 LOAD_CONST 4 ('Finally')
54 CALL_FUNCTION 1 (1 positional, 0 keyword pair)
57 POP_TOP
9 58 LOAD_CONST 5 (False)
61 RETURN_VALUE
62 END_FINALLY
10 63 LOAD_CONST 0 (None)
66 RETURN_VALUE
--
Terry Jan Reedy
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