chadrik commented on a change in pull request #11038: [BEAM-7746] More typing
fixes
URL: https://github.com/apache/beam/pull/11038#discussion_r396690657
##########
File path: sdks/python/apache_beam/transforms/core.py
##########
@@ -1300,12 +1300,13 @@ def to_runner_api_parameter(self, context):
common_urns.requirements.REQUIRES_STATEFUL_PROCESSING.urn)
from apache_beam.runners.common import DoFnSignature
sig = DoFnSignature(self.fn)
- is_splittable = sig.is_splittable_dofn()
Review comment:
> Not sure if checking get_restriction_coder() return type instead of
is_splittable_dofn() is future proof.
`get_restriction_coder()` calls `is_splittable_dofn()` and returns `None` if
it's not splittable. So I interpreted a `None` result from this method to mean
"is not splittable".
```python
def get_restriction_coder(self):
# type: () -> Optional[TupleCoder]
"""Get coder for a restriction when processing an SDF. """
if self.is_splittable_dofn():
return TupleCoder([
(self.get_restriction_provider().restriction_coder()),
(self.get_watermark_estimator_provider().estimator_state_coder())
])
else:
return None
```
> I don't understand the change, from a mypy correctness perspective.
Here's the problem:
```python
if is_splittable:
restriction_coder = sig.get_restriction_coder() # returns
Optional[TupleCoder]
restriction_coder_id = context.coders.get_id(restriction_coder) #
does not accept Optional!
else:
restriction_coder_id = None
```
With my changes, we naturally drop the optionality before passing the value
to `context.coders.get_id()`. We also avoid a redundant call to
`is_splittable_dofn()`, FWIW.
I see two options:
1) keep my changes and update the documentation of `get_restriction_coder()`
to clarify that `None` result indicates "is not splittable"
2) revert my changes and add `assert restriction_coder is None` before the
call to `context.coders.get_id()`
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