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gh-157710: Avoid copy for large int in PyUnicodeWriter_WriteStr() by vstinner · Pull Request #158448 · python/cpython · GitHub

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gh-157710: Avoid copy for large int in PyUnicodeWriter_WriteStr() #158448

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Merged
vstinner merged 1 commit into from
Sep 29, 2026
+29 −4
Conversation 0 Commits 1 Checks 57 Files changed 2
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gh-157710: Avoid copy for large int in PyUnicodeWriter_WriteStr() #158448

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29 changes: 29 additions & 0 deletions Lib/test/test_capi/test_unicode.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2262,6 +2262,35 @@ def __repr__(self):
self.assertEqual(writer.get_buffer(), expected)
self.assertIs(writer.finish(), unique_string)

def test_readonly_optim_large_int(self):
# Read-only optimization in _PyLong_FormatWriter() for large integer:
# use _pylong.int_to_decimal_string() result as a read-only string.
# See pylong_int_to_decimal_string().

self.addCleanup(sys.set_int_max_str_digits,
sys.get_int_max_str_digits())
sys.set_int_max_str_digits(0)

# _PyLong_FormatWriter() calls _pylong.int_to_decimal_string() for
# integer with Py_SIZE() > 1000.
large_int = 1 << (sys.int_info.bits_per_digit * 1020)
large_int_str = str(large_int)
expected = (len(large_int_str), 127, True)

for size in (0, 123):
with self.subTest(size=size):
# Test PyUnicodeWriter_WriteStr()
writer = self.create_writer(size)
writer.write_str(large_int)
self.assertEqual(writer.get_buffer(), expected)
self.assertEqual(writer.finish(), large_int_str)

# Test PyUnicodeWriter_WriteRepr()
writer = self.create_writer(size)
writer.write_repr(large_int)
self.assertEqual(writer.get_buffer(), expected)
self.assertEqual(writer.finish(), large_int_str)


# Test PyUnicodeWriter_Format()
@unittest.skipIf(ctypes is None, 'need ctypes')
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4 changes: 0 additions & 4 deletions Objects/longobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2045,10 +2045,6 @@ pylong_int_to_decimal_string(PyObject *aa,
goto error;
}
if (writer) {
Py_ssize_t size = PyUnicode_GET_LENGTH(s);
if (_PyUnicodeWriter_Prepare(writer, size, '9') == -1) {
goto error;
}
if (_PyUnicodeWriter_WriteStr(writer, s) < 0) {
goto error;
}
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