gh-146238: add missing tests for 'e', 'Zf' and 'Zd' array type codes in test_buffer.py

[skirpichev]

This amends e79fd60.

• Issue: Support half-floats in the array module #146238

[skirpichev]

CC @vstinner

[vstinner]

You already skipped formats larger than MAX_ALIGN in cases = [array.array(fmt) for fmt in ARRAY if struct.calcsize(fmt) <= MAX_ALIGN], no?

[vstinner]

I suggest adding a comment explaining why we skip some formats:

Suggested change

	align = max(struct.calcsize(fmt) for fmt in ARRAY
	if struct.calcsize(fmt) <= MAX_ALIGN)
	cases = [array.array(fmt) for fmt in ARRAY
	if struct.calcsize(fmt) <= MAX_ALIGN]
	# Skip formats larger than the normal alignment of 'max_align_t',
	# in bytes.
	formats = [fmt for fmt in ARRAY if struct.calcsize(fmt) <= MAX_ALIGN]
	align = max(struct.calcsize(fmt) for fmt in formats)
	cases = [array.array(fmt) for fmt in formats]

[vstinner]

I suggest only building the list once, replace not k in with k not in, replace k with fmt and add missing array formats (uw and qQ):

# Format codes supported by array.array
ARRAY = NATIVE.copy()
_ARRAY_FORMATS = list("bBuwhHiIlLqQefd") + ['Zf', 'Zd']
for fmt in NATIVE:
    if fmt not in _ARRAY_FORMATS:
        del ARRAY[fmt]

[vstinner]

test_buffer fails on WASI:

FAIL: test_array_alignment (test.test_buffer.TestBufferProtocol.test_array_alignment)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Lib/test/test_buffer.py", line 4514, in test_array_alignment
    self.assertEqual(
    ~~~~~~~~~~~~~~~~^
        [_testcapi.buffer_pointer_as_int(case) % align for case in cases],
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        [0] * len(cases),
        ^^^^^^^^^^^^^^^^^
    )
    ^
AssertionError: Lists differ: [8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8] != [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

First differing element 0:
8
0

- [8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8]
+ [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

[vstinner]

On WASI, ALIGNOF_MAX_ALIGN_T is 16 bytes and struct.calcsize("Zd") is 16 bytes. WASI is a 32-bit platform (sys.maxsize is 2147483647). Maybe we should only test formats up to 4 bytes?

Would it make sense to use MAX_ALIGN = struct.calcsize('P')?