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Re: Try-except-finally paradox

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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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Try-except-finally paradox Jessica Ross <deathweasel@gmail.com> - 2014-01-29 21:56 -0800
  Re: Try-except-finally paradox Ian Kelly <ian.g.kelly@gmail.com> - 2014-01-29 23:23 -0700
  Re: Try-except-finally paradox Andrew Berg <robotsondrugs@gmail.com> - 2014-01-30 00:33 -0600
    Re: Try-except-finally paradox Rotwang <sg552@hotmail.co.uk> - 2014-01-30 18:12 +0000
      Re: Try-except-finally paradox Ethan Furman <ethan@stoneleaf.us> - 2014-01-30 10:30 -0800
  Re: Try-except-finally paradox wxjmfauth@gmail.com - 2014-01-29 22:59 -0800
  Re:Try-except-finally paradox Dave Angel <davea@davea.name> - 2014-01-30 07:05 -0500
  Re: Try-except-finally paradox Chris Angelico <rosuav@gmail.com> - 2014-01-31 00:02 +1100
  Re: Try-except-finally paradox MRAB <python@mrabarnett.plus.com> - 2014-01-30 13:11 +0000
  Re: Try-except-finally paradox Chris Angelico <rosuav@gmail.com> - 2014-01-31 00:19 +1100
  Re: Try-except-finally paradox Terry Reedy <tjreedy@udel.edu> - 2014-01-31 00:26 -0500
  Re: Try-except-finally paradox Göktuğ Kayaalp <self@gkayaalp.com> - 2014-02-01 03:58 +0200

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