https://github.com/python/cpython/commit/011179a79a0d7b93ce074b25b0819e96b6dd3315
commit: 011179a79a0d7b93ce074b25b0819e96b6dd3315
branch: main
author: Sergey B Kirpichev <[email protected]>
committer: vstinner <[email protected]>
date: 2025-09-11T12:30:53+02:00
summary:
gh-71810: Fix corner case (length==0) for int.to_bytes() (#138739)
```pycon
>>> (0).to_bytes(0, 'big', signed=True)
b''
>>> (-1).to_bytes(0, 'big', signed=True) # was b''
Traceback (most recent call last):
File "<python-input-0>", line 1, in <module>
(-1).to_bytes(0, 'big', signed=True)
~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
OverflowError: int too big to convert
```
Co-authored-by: Serhiy Storchaka <[email protected]>
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-09-10-14-53-59.gh-issue-71810.ppf0J-.rst
M Lib/test/test_long.py
M Objects/longobject.c
diff --git a/Lib/test/test_long.py b/Lib/test/test_long.py
index d63bc19ed9c9a2..b48a8812a1a2d1 100644
--- a/Lib/test/test_long.py
+++ b/Lib/test/test_long.py
@@ -1374,17 +1374,22 @@ def equivalent_python(n, length, byteorder,
signed=False):
check(tests4, 'little', signed=False)
self.assertRaises(OverflowError, (256).to_bytes, 1, 'big',
signed=False)
- self.assertRaises(OverflowError, (256).to_bytes, 1, 'big', signed=True)
self.assertRaises(OverflowError, (256).to_bytes, 1, 'little',
signed=False)
- self.assertRaises(OverflowError, (256).to_bytes, 1, 'little',
signed=True)
+ self.assertRaises(OverflowError, (128).to_bytes, 1, 'big', signed=True)
+ self.assertRaises(OverflowError, (128).to_bytes, 1, 'little',
signed=True)
+ self.assertRaises(OverflowError, (-129).to_bytes, 1, 'big',
signed=True)
+ self.assertRaises(OverflowError, (-129).to_bytes, 1, 'little',
signed=True)
self.assertRaises(OverflowError, (-1).to_bytes, 2, 'big', signed=False)
self.assertRaises(OverflowError, (-1).to_bytes, 2, 'little',
signed=False)
self.assertEqual((0).to_bytes(0, 'big'), b'')
+ self.assertEqual((0).to_bytes(0, 'big', signed=True), b'')
self.assertEqual((1).to_bytes(5, 'big'), b'\x00\x00\x00\x00\x01')
self.assertEqual((0).to_bytes(5, 'big'), b'\x00\x00\x00\x00\x00')
self.assertEqual((-1).to_bytes(5, 'big', signed=True),
b'\xff\xff\xff\xff\xff')
self.assertRaises(OverflowError, (1).to_bytes, 0, 'big')
+ self.assertRaises(OverflowError, (-1).to_bytes, 0, 'big', signed=True)
+ self.assertRaises(OverflowError, (-1).to_bytes, 0, 'little',
signed=True)
# gh-98783
class SubStr(str):
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-09-10-14-53-59.gh-issue-71810.ppf0J-.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-09-10-14-53-59.gh-issue-71810.ppf0J-.rst
new file mode 100644
index 00000000000000..a87db44225e825
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-09-10-14-53-59.gh-issue-71810.ppf0J-.rst
@@ -0,0 +1,2 @@
+Raise :exc:`OverflowError` for ``(-1).to_bytes()`` for signed conversions
+when bytes count is zero. Patch by Sergey B Kirpichev.
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 287458ba2da62a..63b48572ff20d3 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -1209,7 +1209,7 @@ _PyLong_AsByteArray(PyLongObject* v,
*p = (unsigned char)(accum & 0xff);
p += pincr;
}
- else if (j == n && n > 0 && is_signed) {
+ else if (j == n && is_signed) {
/* The main loop filled the byte array exactly, so the code
just above didn't get to ensure there's a sign bit, and the
loop below wouldn't add one either. Make sure a sign bit
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