On Tue, Oct 15, 2013 at 12:31 PM, Mark Janssen
<dreamingforw...@gmail.com> wrote:
>> Python objects have dynamic operations suited
>> to a naive interpreter like CPython.
>
> Naive, no.
>
"Naive", in this instance, means executing code exactly as written,
without optimizing things (and it's not an insult, btw). For instance,
a C compiler might turn this into simple register operations:
int x=5;
int foo()
{
x+=3;
return x*2;
}
The two references to 'x' inside foo() can safely be assumed to be the
same 'x', and the value as written by the += MUST be the one used to
calculate *2. If you declare x to be volatile, that assumption won't
be made, and the interpretation will be naive. Now here's the CPython
equivalent:
x=5
def foo():
global x
x+=3
return x*2
>>> dis.dis(foo)
3 0 LOAD_GLOBAL 0 (x)
3 LOAD_CONST 1 (3)
6 INPLACE_ADD
7 STORE_GLOBAL 0 (x)
4 10 LOAD_GLOBAL 0 (x)
13 LOAD_CONST 2 (2)
16 BINARY_MULTIPLY
17 RETURN_VALUE
Note that the global is stored, then reloaded. This is the naive
approach, assuming nothing about the relations between operations.
It's an easy way to be thread-safe, it just costs performance.
ChrisA
--
https://mail.python.org/mailman/listinfo/python-list
