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gh-158500: Reject trailing characters in date.fromisoformat #158557

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gh-158500: Reject trailing characters in date.fromisoformat #158557

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897999d
gh-158500: Reject trailing date characters
rupayon123 Oct 1, 2026
57801f4
gh-158500: Cover multibyte trailing date data
rupayon123 Oct 1, 2026
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6 changes: 6 additions & 0 deletions Lib/_pydatetime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -389,6 +389,9 @@ def _parse_isoformat_date(dtstr):
pos += has_sep

dayno = _read_isoformat_component(dtstr[pos:pos + 1], 1)
pos += 1
if pos != len(dtstr):
raise ValueError("Invalid isoformat string")

return list(_isoweek_to_gregorian(year, weekno, dayno))
else:
Expand All @@ -399,6 +402,9 @@ def _parse_isoformat_date(dtstr):

pos += has_sep
day = _read_isoformat_component(dtstr[pos:pos + 2], 2)
pos += 2
if pos != len(dtstr):
raise ValueError("Invalid isoformat string")

return [year, month, day]

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5 changes: 5 additions & 0 deletions Lib/test/datetimetester.py
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Expand Up @@ -2114,9 +2114,14 @@ def test_fromisoformat_fails(self):
'2020-W 5', # space in the week number
'2020061', # 7 chars: day slice reads a 1-character tail
'2020-W2', # 1-digit week number
'2020010112', # Trailing characters after a basic-format date
'2020W011xx', # Trailing characters after a basic-format week date
'٢025-03-09', # Unicode characters
'2009\ud80002\ud80028', # Separators are surrogate codepoints
]
if not issubclass(self.theclass, datetime):
# 9 characters, 10 UTF-8 bytes; exercise the C parser's 10-byte path.
bad_strs.append('20200101\u00e9')

for bad_str in bad_strs:
with self.assertRaises(ValueError):
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-10-01-04-30-00.gh-issue-158500.a1b2c3.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix :meth:`datetime.date.fromisoformat` accepting basic-format date strings
with trailing characters.
7 changes: 7 additions & 0 deletions Modules/_datetimemodule.c
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Expand Up @@ -991,6 +991,10 @@ parse_isoformat_date(const char *dtstr, const size_t len, int *year, int *month,
iso_day = 1;
}

if ((size_t)(p - dtstr) != len) {
return -1;
}

int rv = iso_to_ymd(*year, iso_week, iso_day, year, month, day);
if (rv) {
return -3 + rv;
Expand All @@ -1011,6 +1015,9 @@ parse_isoformat_date(const char *dtstr, const size_t len, int *year, int *month,
if (p == NULL) {
return -1;
}
if ((size_t)(p - dtstr) != len) {
return -1;
}
return 0;
}

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