Try-except-finally paradox
Rotwang
sg552 at hotmail.co.uk
Thu Jan 30 13:12:38 EST 2014
On 30/01/2014 06:33, Andrew Berg wrote:
> On 2014.01.29 23:56, Jessica Ross wrote:
>> 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?
>>
> My guess would be that the interpreter doesn't let the finally block
> get skipped under any circumstances, so the return value gets set to
> True, but then it forces the finally block to be run before returning,
> which changes the return value to False.
Mine too. We can check that the interpreter gets as far as evaluating
the return value in the except block:
>>> def paradox2():
try:
raise Exception("Raise")
except:
print("Except")
return [print("Return"), True][1]
finally:
print("Finally")
return False
return None
>>> ret = paradox2()
Except
Return
Finally
>>> ret
False
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