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gh-111140: Improve PyLong_AsNativeBytes API doc example & improve the test (#115380)

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This expands the examples to cover both realistic use cases for the API.
    
I noticed thing in the test that could be done better so I added those as well: We need to guarantee that all bytes of the result are overwritten and that too many are not written.  Tests now pre-fills the result with data in order to ensure that.

Co-authored-by: Steve Dower <steve.dower@microsoft.com>
This commit is contained in:
Gregory P. Smith 2024-02-21 19:27:16 -08:00 • committed by GitHub
parent 7f5e3f04f8
commit fac99b8b0d
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2 changed files with 82 additions and 22 deletions
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30
Lib/test/test_capi/test_long.py
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@ -438,7 +438,12 @@ class LongTests(unittest.TestCase):
if support.verbose:
print(f"SIZEOF_SIZE={SZ}\n{MAX_SSIZE=:016X}\n{MAX_USIZE=:016X}")
# These tests check that the requested buffer size is correct
# These tests check that the requested buffer size is correct.
# This matches our current implementation: We only specify that the
# return value is a size *sufficient* to hold the result when queried
# using n_bytes=0. If our implementation changes, feel free to update
# the expectations here -- or loosen them to be range checks.
# (i.e. 0 *could* be stored in 1 byte and 512 in 2)
for v, expect in [
(0, SZ),
(512, SZ),
@ -453,12 +458,25 @@ class LongTests(unittest.TestCase):
(-(2**256-1), 33),
]:
with self.subTest(f"sizeof-{v:X}"):
buffer = bytearray(1)
buffer = bytearray(b"\x5a")
self.assertEqual(expect, asnativebytes(v, buffer, 0, -1),
"PyLong_AsNativeBytes(v, NULL, 0, -1)")
"PyLong_AsNativeBytes(v, <unknown>, 0, -1)")
self.assertEqual(buffer, b"\x5a",
"buffer overwritten when it should not have been")
# Also check via the __index__ path
self.assertEqual(expect, asnativebytes(Index(v), buffer, 0, -1),
"PyLong_AsNativeBytes(Index(v), NULL, 0, -1)")
"PyLong_AsNativeBytes(Index(v), <unknown>, 0, -1)")
self.assertEqual(buffer, b"\x5a",
"buffer overwritten when it should not have been")
# Test that we populate n=2 bytes but do not overwrite more.
buffer = bytearray(b"\x99"*3)
self.assertEqual(2, asnativebytes(4, buffer, 2, 0), # BE
"PyLong_AsNativeBytes(v, <3 byte buffer>, 2, 0) // BE")
self.assertEqual(buffer, b"\x00\x04\x99")
self.assertEqual(2, asnativebytes(4, buffer, 2, 1), # LE
"PyLong_AsNativeBytes(v, <3 byte buffer>, 2, 1) // LE")
self.assertEqual(buffer, b"\x04\x00\x99")
# We request as many bytes as `expect_be` contains, and always check
# the result (both big and little endian). We check the return value
@ -510,7 +528,9 @@ class LongTests(unittest.TestCase):
]:
with self.subTest(f"{v:X}-{len(expect_be)}bytes"):
n = len(expect_be)
buffer = bytearray(n)
# Fill the buffer with dummy data to ensure all bytes
# are overwritten.
buffer = bytearray(b"\xa5"*n)
expect_le = expect_be[::-1]
self.assertEqual(expect_n, asnativebytes(v, buffer, n, 0),