## Cause
Until 3.11, fromisoformat only accepted formats emitted by date.isoformat/datetime.isoformat (which do not use Z); 3.11 docs document broader ISO 8601 acceptance including '2011-11-04T00:05:23Z' → UTC.
## Steps
1. Confirm interpreter version (sys.version_info) in the failing environment.
2. If stuck on <=3.10, preprocess: ts = s[:-1] + '+00:00' if s.endswith('Z') else s before fromisoformat(ts).
3. Alternatively use dateutil.parser.isoparse(s) with python-dateutil dependency.
4. Long-term: upgrade runtime image/requirements to Python >=3.11.
5. Add a regression test with a literal '...Z' timestamp on the minimum supported Python.
## Expected result
Timestamps ending in Z parse to timezone-aware UTC datetimes without ValueError.
## Misleading approaches
- Stripping Z without adding an explicit offset (produces naive datetimes).
- Assuming strptime %z accepts Z without conversion on 3.10.
## Limitations
- Manual Z→+00:00 substitution does not cover every non-isoformat ISO 8601 edge case 3.10 rejects.
- dateutil adds a third-party dependency if not already present.
## Unknowns
- Whether fractional-second variants beyond documented examples behave identically across all <=3.10 patch releases without local testing.
## Evidence claims
- (documented_platform_behavior) CPython 3.10 fromisoformat does not claim support for arbitrary ISO 8601 including Z suffix. — https://raw.githubusercontent.com/python/cpython/22344e9d4ba2a966ca17c9a1ca78c4c1defc3f09/Doc/library/datetime.rst
- (released_fix) CPython 3.11+ documents fromisoformat accepting '2011-11-04T00:05:23Z' as UTC. — https://raw.githubusercontent.com/python/cpython/ca0cdf42cf2181c345739bc0e24c8ff771bd8c38/Doc/library/datetime.rst
- (released_fix) The 3.11 change note states prior versions only supported isoformat-emitted formats. — https://raw.githubusercontent.com/python/cpython/ca0cdf42cf2181c345739bc0e24c8ff771bd8c38/Doc/library/datetime.rst
Proposed approach
- Problem id
- 68377736-80f9-4749-bd78-61c64080e35f
- Proposed action
- Prefer running on Python 3.11+ where fromisoformat accepts Z. On 3.10 and older, normalize Z to +00:00 before fromisoformat, or parse with dateutil.parser.isoparse or a library that fully supports ISO 8601.
- Applicability
- State
- partial
- Text
- Code calling datetime.fromisoformat on UTC timestamps with Z suffix in containers or CI pinned to Python <=3.10 while dev machines use 3.11+.; affected: CPython 3.7 through 3.10 for Z-suffix timestamps via fromisoformat; fixed: CPython 3.11; fix_status: CONFIRMED_SOLUTION
- Limitations
- State
- partial
- Text
- Manual Z→+00:00 substitution does not cover every non-isoformat ISO 8601 edge case 3.10 rejects. dateutil adds a third-party dependency if not already present.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- Code calling datetime.fromisoformat on UTC timestamps with Z suffix in containers or CI pinned t
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