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https://issues.apache.org/jira/browse/BEAM-6695?focusedWorklogId=236533&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-236533
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ASF GitHub Bot logged work on BEAM-6695:
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Author: ASF GitHub Bot
Created on: 02/May/19 20:14
Start Date: 02/May/19 20:14
Worklog Time Spent: 10m
Work Description: ttanay commented on issue #8206: [BEAM-6695] Latest
PTransform for Python SDK
URL: https://github.com/apache/beam/pull/8206#issuecomment-488815622
@aaltay @robinyqiu
I agree that `_check_instance_type` is not the way to go.
The need for type validation inside the staticmethod `add_timestamp` of
PerKey exists because when using `with_input_types`, the type evaluation does
not evaluate PCollections of WindowedValue correctly as needed in this case -
the value attribute of a WindowedValue.
Eg:
This is from the test:
[test_per_key](https://github.com/ttanay/beam/blob/beam-6695/sdks/python/apache_beam/transforms/combiners_test.py#L415)
```python
# Elements to create PCollection from
elem_list = [window.GlobalWindows.windowed_value(('a', 1), 300),
window.GlobalWindows.windowed_value(('b', 3), 100),
window.GlobalWindows.windowed_value(('a', 2), 200)]
with TestPipeline() as p:
pc = p | Create(elem_list)
latest = pc | combine.Latest.PerKey()
assert_that(latest, equal_to([('a', 1), ('b', 3)]))
```
In the staticmethod `add_timestamp` of Latest PTransform, the type of `pc`
is evaluated as WindowedValue when using `with_input_types`, whereas, it should
be KV since the value attribute of the WindowedValue object is a KV(`('a', 1)`)
which is the case when using `_check_instance_type`.
Is this expected behaviour? If not, I'd love to fix this. It would solve the
problem.
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Issue Time Tracking
-------------------
Worklog Id: (was: 236533)
Time Spent: 7.5h (was: 7h 20m)
> Latest transform for Python SDK
> -------------------------------
>
> Key: BEAM-6695
> URL: https://issues.apache.org/jira/browse/BEAM-6695
> Project: Beam
> Issue Type: New Feature
> Components: sdk-py-core
> Reporter: Ahmet Altay
> Assignee: Tanay Tummalapalli
> Priority: Minor
> Time Spent: 7.5h
> Remaining Estimate: 0h
>
> Add a PTransform} and Combine.CombineFn for computing the latest element in a
> PCollection.
> It should offer the same API as its Java counterpart:
> https://github.com/apache/beam/blob/11a977b8b26eff2274d706541127c19dc93131a2/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Latest.java
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