Awkwardness of C API for making tuples

[John Machin]

Dave Opstad wrote:
> One of the functions in a C extension I'm writing needs to return a
> tuple of integers, where the length of the tuple is only known at
> runtime. I'm currently doing a loop calling PyInt_FromLong to make
the
> integers,

What is the purpose of this first loop?

In what variable-length storage are you storing these (Python) integers
during this first loop? Something you created with (a) PyMem_Malloc (b)
malloc (c) alloca (d) your_own_malloc?

> then PyTuple_New, and finally a loop calling PyTuple_SET_ITEM
> to set the tuple's items. Whew.

Whew indeed.

> Does anyone know of a simpler way? I can't use Py_BuildValue because
I
> don't know at compile-time how many values there are going to be. And

> there doesn't seem to be a PyTuple_FromArray() function.
>
> If I'm overlooking something obvious, please clue me in!

1. Determine the length of the required tuple; this may need a loop,
but only to _count_ the number of C longs that you have.
2. Use PyTuple_New.
3. Loop to fill the tuple, using PyInt_FromLong and PyTuple_SetItem.

Much later, after thoroughly testing your code, gingerly change
PyTuple_SetItem to PyTuple_SET_ITEM. Benchmark the difference. Is it
anywhere near what you saved by cutting out the store_in_temp_array
thing in the first loop?