On Tue, Jun 25, 2013 at 11:35 AM, Peter Otten <__pete...@web.de> wrote:
> eryksun wrote:
>
>> Constant folding for binary operations has a length limit of 20 for
>> sequences:
>>
>> >>> dis.dis(lambda: '0123456789' + '0123456789' + '0')
>> 1 0 LOAD_CONST 3 ('0123456789
>> 0123456789')
>> 3 LOAD_CONST 2 ('0')
>> 6 BINARY_ADD
>> 7 RETURN_VALUE
>
> Interesting. Do you know why the limit is so low (especially for strings)?
It isn't special-cased for strings. It just checks for a sequence
length in general. The idea is to limit the size of .pyc files. Quote:
If the new constant is a sequence, only folds when the size
is below a threshold value. That keeps pyc files from
becoming large in the presence of code like: (None,)*1000.
The threshold of 20 isn't a tunable parameter. It's hard-coded in the source:
size = PyObject_Size(newconst);
if (size == -1)
PyErr_Clear();
else if (size > 20) {
Py_DECREF(newconst);
return 0;
}
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