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Sun Oct 25 16:10:39 EDT 2015 · https://mail.python.org/pipermail/python-dev/2015-October/142025.html

Thank you for your confirmation,

I am going to read the devguide.

> On 25 oct. 2015, at 7:50 PM, Raymond Hettinger <raymond.hettinger at gmail.com> wrote:
> 
> 
>>> On Oct 25, 2015, at 12:33 PM, Raymond Hettinger <raymond.hettinger at gmail.com> wrote:
>>> 
>>> On Oct 22, 2015, at 10:02 AM, Brett Cannon <brett at python.org> wrote:
>>> 
>>> So my question is, the byte code generator removes the unused functions, variables etc…, is it right?
>>> 
>>> Technically the peepholer removes the dead branch, but since the peepholer is run on all bytecode you can't avoid it.
>> 
>> IIRC, the code was never generated in the first place (before the peephole pass).  This used to be true before the AST branch was added and I think it may still be true.
> 
> I just verified this.  So Brett's post was incorrect and misleading.
> 
> 
> Raymond
> 
> 
> ----------- Verify by turning-off the optimizations ----------
> cpython $ hg diff Python/peephole.c
> diff --git a/Python/peephole.c b/Python/peephole.c
> --- a/Python/peephole.c
> +++ b/Python/peephole.c
> @@ -383,7 +383,7 @@
>     /* Avoid situations where jump retargeting could overflow */
>     assert(PyBytes_Check(code));
>     codelen = PyBytes_GET_SIZE(code);
> -    if (codelen > 32700)
> +    if (codelen > 0)
>         goto exitUnchanged;
> 
> -------- Then run a simple disassembly -----------------------
> 
> from dis import dis
> 
> def f(x):
>    if 0:
>        print('First')
>    print('Second')
> 
> dis(f)
> 
> -------- The output is ---------------------------------------------------
> 
> $ py tmp.py
>  6           0 LOAD_GLOBAL              0 (print)
>              3 LOAD_CONST               1 ('Second')
>              6 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
>              9 POP_TOP
>             10 LOAD_CONST               0 (None)
>             13 RETURN_VALUE
> 

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