On 5/1/2017 5:50 AM, Serhiy Storchaka wrote:
I want to add promises to public C API functions that create trivial
instances of immutable basic types (integers 0 and 1, empty tuple,
string and bytes object) -- PyLong_FromLong(0), PyLong_FromLong(1),
PyTuple_New(0), PyUnicode_FromStringAndSize(NULL, 0),
PyUnicode_FromString(""), PyBytes_FromStringAndSize(NULL, 0),
PyBytes_FromString("") -- that they always succeed and never return
NULL. Currently they always or almost always succeed, but this is an
implementation detail. I want to make this promise official and more
strong, so that it is true even at very early stage of the interpreter
intitalization and at very late stage of the finalization. Also I want
to add private references to singletons that represent these values
(_PyLong_Zero, _PyTuple_Empty, etc) similar to Py_None and Py_True.
This could make some code clearer. For example see [1] and [2].
These promises add limitations for future changes of the interpreter,
but the official promise decreases the probability of unintentional
changes that break implicit properties.
The promise makes it clear that breaking the property is a bug to be
fixed. It only decreases the probability for someone who has read the
promise. Unfortunately, 'never fail' is hard to test ;-).
Do I have the right to give such promises?
By yourself, I would think not. With a couple of coredev concurrences,
and none against, maybe. But I think the following does need to be
asked publicly, here, so implementors of CPython alternatives have a
chance to respond.
> Are there any reasons that might prevent their implementation?
If the answer is no, I think the simplifications in the following are a
good argument for the change. On the other hand, I have to wonder why
there were not made previously.
[1] https://bugs.python.org/issue29878
[2] https://bugs.python.org/issue30162
--
Terry Jan Reedy
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