Patrick539 opened a new issue, #70762:
URL: https://github.com/apache/airflow/issues/70762
### Under which category would you file this issue?
Task SDK
### Apache Airflow version
3.3.0
### What happened and how to reproduce it?
** Issue Description **
StartOfDayMapper defaults input_format to "%Y-%m-%dT%H:%M:%S". If an
upstream asset emits a partition key that's already at day granularity (e.g.
"2026-07-30"), calling to_downstream() without explicitly overriding
input_format raises an error.
As a result, the mapper must be explicitly configured with the correct
input_format up front. This prevents flexible handling of a mix of partition
keys at different granularities (e.g. some upstream assets emitting day-level
keys, others hour-level) without requiring separate, explicitly-configured
mapper instances for each.
** Repro **
from airflow.partition_mappers.temporal import StartOfDayMapper
# --- Case 1: full timestamp input (matches the default input_format) ---
mapper = StartOfDayMapper() # default input_format="%Y-%m-%dT%H:%M:%S"
print(mapper.to_downstream("2026-07-30T14:22:05")) # → "2026-07-30"
# --- Case 2: date-only input (works) ---
mapper_date_only = StartOfDayMapper(input_format="%Y-%m-%d")
print(mapper_date_only.to_downstream("2026-07-30")) # → "2026-07-30"
# --- Case 3: date-only input WITHOUT telling it the format (reproduces the
error) ---
mapper_default = StartOfDayMapper() # still expects full timestamp
print(
mapper_default.to_downstream("2026-07-30")
) # → ValueError: time data '2026-07-30' does not match format
'%Y-%m-%dT%H:%M:%S'
### What you think should happen instead?
Either:
Partition keys already at day granularity should be passed through
unchanged, similar to IdentityMapper,
or
StartOfDayMapper should output keys in its own default input_format (i.e.
"%Y-%m-%dT%H:%M:%S", with the time component zeroed to T00:00:00), so that its
output can be fed back into another instance of the same mapper (chaining).
### Operating System
_No response_
### Deployment
None
### Apache Airflow Provider(s)
_No response_
### Versions of Apache Airflow Providers
_No response_
### Official Helm Chart version
Not Applicable
### Kubernetes Version
_No response_
### Helm Chart configuration
_No response_
### Docker Image customizations
_No response_
### Anything else?
_No response_
### Are you willing to submit PR?
- [ ] Yes I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
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