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gh-159739: Reject the minimum dynamic formatting width #159780

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Merged
JelleZijlstra merged 1 commit into from
Oct 20, 2026
Merged

gh-159739: Reject the minimum dynamic formatting width #159780

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2 changes: 2 additions & 0 deletions Lib/test/test_format.py
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Original file line number Diff line number Diff line change
Expand Up @@ -324,6 +324,8 @@ def test_common_format(self):
"format argument 1: too big for width")
test_exc_common('%*r', (-2**1000, 1), OverflowError,
"format argument 1: too big for width")
test_exc_common('%*r', (-maxsize - 1, 1), OverflowError,
"format argument 1: too big for width")
test_exc_common('%.*r', (2**1000, 1), OverflowError,
"format argument 1: too big for precision")
test_exc_common('%.*r', (-2**1000, 1), OverflowError,
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-10-19-20-38-17.gh-issue-159739.78e530.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Raise :exc:`OverflowError` when the absolute value of a dynamic printf-style
formatting width is too large.
4 changes: 4 additions & 0 deletions Objects/bytesobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -852,6 +852,10 @@ _PyBytes_FormatEx(const char *format, Py_ssize_t format_len,
goto error;
}
if (width < 0) {
if (width == PY_SSIZE_T_MIN) {
FORMAT_ERROR(PyExc_OverflowError, "too big for width%s", "");
goto error;
}
flags |= F_LJUST;
width = -width;
}
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4 changes: 4 additions & 0 deletions Objects/unicode_format.c
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Original file line number Diff line number Diff line change
Expand Up @@ -564,6 +564,10 @@ unicode_format_arg_parse(struct unicode_formatter_t *ctx,
return -1;
}
if (arg->width < 0) {
if (arg->width == PY_SSIZE_T_MIN) {
FORMAT_ERROR(PyExc_OverflowError, "too big for width%s", "");
return -1;
}
arg->flags |= F_LJUST;
arg->width = -arg->width;
}
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