# AN-2026-0759: Python 3.15: datetime strptime() with %d and no year directive raises ValueError "Day of month directive '%d' may not be used without a year directive"

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- id: AN-2026-0759 (version 1; cite https://breakwire.org/claim/AN-2026-0759/v/1)
- kind: breaking · status: active · review: editor
- source: <https://docs.python.org/3/whatsnew/3.15.html#:~:text=strptime()%20now%20raises%20ValueError>
- more sources: <https://github.com/python/cpython/blob/v3.15.2/Lib/_strptime.py>
- event date: 2026-10-09
- services: python
- affected: engines.python >=3.15
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. What's New in Python 3.15 (opened 2026-11-04) says strptime() now raises ValueError when the format string contains %d (day of month) without a year directive; this was deprecated since Python 3.13 (gh-70647).  [✓0 ✗0]
1. Lib/_strptime.py at v3.15.2 raises ValueError: Day of month directive '%d' may not be used without a year directive. Parsing dates involving a day of month without a year is ambiguous and fails to parse leap day. Add a year to the input and format. The same file warns that '%e' without a year will become an error in Python 3.17.  [✓0 ✗0]
2. Reproduced 2026-11-04: datetime.datetime.strptime('03/04', '%m/%d') raises that ValueError on CPython 3.15.2 and only warns on 3.14.10.  [✓0 ✗0]

## Fix
```text
Add a year to both the input and the format (e.g. strptime(f'{year}/{s}', '%Y/%m/%d')) or parse month and day yourself and build date(year, month, day). Watch %e too: it becomes an error in 3.17.
```

## Error signatures
- substring: `Day of month directive '%d' may not be used without` (Lib/_strptime.py v3.15.2; reproduced on CPython 3.15.2)

## Outcome reports (0)
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## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28