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gh-107779: Check for the separator between date and time in datetime.datetime.fromisoformat #107791

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gh-107779: Check for the separator between date and time in datetime.datetime.fromisoformat #107791

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7 changes: 6 additions & 1 deletion Lib/_pydatetime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1862,13 +1862,18 @@ def fromisoformat(cls, date_string):
try:
separator_location = _find_isoformat_datetime_separator(date_string)
dstr = date_string[0:separator_location]
tstr = date_string[(separator_location+1):]
sep = date_string[separator_location:separator_location+1]
tstr = date_string[separator_location+1:]

date_components = _parse_isoformat_date(dstr)
except ValueError:
raise ValueError(
f'Invalid isoformat string: {date_string!r}') from None

if sep and (_is_ascii_digit(sep) or not tstr):
# Date and time most likely split at the wrong place, indicates wrong format.
raise ValueError(f'Invalid isoformat string: {date_string!r}')

if tstr:
try:
time_components = _parse_isoformat_time(tstr)
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3 changes: 3 additions & 0 deletions Lib/test/datetimetester.py
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Expand Up @@ -1909,6 +1909,7 @@ def test_fromisoformat_fails(self):
'2019-W53-1', # No week 53 in 2019
'2020-W54-1', # No week 54
'2009\ud80002\ud80028', # Separators are surrogate codepoints
'2009-01-01 ', # Trailing separator without time component
]

for bad_str in bad_strs:
Expand Down Expand Up @@ -3295,6 +3296,8 @@ def test_fromisoformat_fails_datetime(self):
'2009-04-19T12:30:45.123456-05:00a', # Extra text
'2009-04-19T12:30:45.123-05:00a', # Extra text
'2009-04-19T12:30:45-05:00a', # Extra text
'2009-04-1912:30:45', # Missing date-time separator 1

@StanFromIreland StanFromIreland Mar 15, 2025

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This is a valid ISO 8601 format...

By mutual agreement of the partners in information interchange, the character [T] may be omitted in
applications where there is no risk of confusing a date and time of day representation with others defined in this International Standard.

'20090419123054', # Missing date-time separator 2
]

for bad_str in bad_strs:
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6 changes: 6 additions & 0 deletions Modules/_datetimemodule.c
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Expand Up @@ -5451,6 +5451,12 @@ datetime_fromisoformat(PyObject *cls, PyObject *dtstr)
if (!rv && len > separator_location) {
// In UTF-8, the length of multi-byte characters is encoded in the MSB
p += separator_location;

if (is_digit(p[0])) {
// Date and time most likely split at the wrong place, indicates wrong format.
goto invalid_string_error;
}

if ((p[0] & 0x80) == 0) {
p += 1;
}
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