On Fri, Mar 14, 2014 at 11:08 AM, Ian Kelly <[email protected]> wrote:
> On Thu, Mar 13, 2014 at 5:55 PM, Chris Angelico <[email protected]> wrote:
>> I'm going to troll for a moment and give you a function that has no
>> return value.
>>
>> def procedure():
>> raise Exception
>
>>>> import dis
>>>> dis.dis(procedure)
> 2 0 LOAD_GLOBAL 0 (Exception)
> 3 RAISE_VARARGS 1
> 6 LOAD_CONST 0 (None)
> 9 RETURN_VALUE
That's a return value in the same way that exec() has a return value
[1]. If somehow the raise fails, it'll return None.
>>>> def get_procedure_return_value():
> ... """Returns the return value of procedure()."""
> ... return procedure.__code__.co_consts[0]
> ...
>>>> print(get_procedure_return_value())
> None
>
> Look, there it is!
Succeeds by coincidence. From what I can see, *every* CPython function
has const slot 0 dedicated to None. At least, I haven't been able to
do otherwise.
>>> def function(x):
return x*2+1
>>> import dis
>>> dis.dis(function)
2 0 LOAD_FAST 0 (x)
3 LOAD_CONST 1 (2)
6 BINARY_MULTIPLY
7 LOAD_CONST 2 (1)
10 BINARY_ADD
11 RETURN_VALUE
>>> function.__code__.co_consts
(None, 2, 1)
Your return value retriever would say it returns None still, but it doesn't.
Trollbridge: you have to pay a troll to cross.
ChrisA
[1] I'm not talking about Python's 'exec' statement, but about the
Unix exec() API, eg execlpe() - see http://linux.die.net/man/3/exec
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