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https://issues.apache.org/jira/browse/BEAM-7746?focusedWorklogId=339087&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-339087
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ASF GitHub Bot logged work on BEAM-7746:
----------------------------------------
Author: ASF GitHub Bot
Created on: 06/Nov/19 00:24
Start Date: 06/Nov/19 00:24
Worklog Time Spent: 10m
Work Description: chadrik commented on pull request #9915: [BEAM-7746]
Add python type hints (part 1)
URL: https://github.com/apache/beam/pull/9915#discussion_r342865083
##########
File path: sdks/python/apache_beam/coders/coder_impl.py
##########
@@ -838,11 +911,12 @@ def encode_to_stream(self, value, out, nested):
out.write_var_int64(0)
def decode_from_stream(self, in_stream, nested):
+ # type: (create_InputStream, bool) -> Sequence
size = in_stream.read_bigendian_int32()
if size >= 0:
elements = [self._elem_coder.decode_from_stream(in_stream, True)
- for _ in range(size)]
+ for _ in range(size)] # type: Iterable[Any]
Review comment:
This is a bit less obvious than that. mypy knows that this is a
`List[Any]`, but below this `element` is rebound to `_ConcatSequence`. Without
this annotation, we get this error:
```
apache_beam/coders/coder_impl.py:935: error: Incompatible types in
assignment (expression has type "_ConcatSequence", variable has type
"List[Any]") [assignment]
```
Here's the full context:
```python
if size >= 0:
elements = [self._elem_coder.decode_from_stream(in_stream, True)
for _ in range(size)] # type: Iterable[Any]
else:
elements = []
count = in_stream.read_var_int64()
while count > 0:
for _ in range(count):
elements.append(self._elem_coder.decode_from_stream(in_stream,
True))
count = in_stream.read_var_int64()
if count == -1:
if self._read_state is None:
raise ValueError(
'Cannot read state-written iterable without state reader.')
state_token = in_stream.read_all(True)
elements = _ConcatSequence(
elements, self._read_state(state_token, self._elem_coder))
```
The first time that a variable appears in the code we can take that
opportunity to relax the type definition, in this case from `List` to
`Iterable`. `_ConcatSequence` is also an `Iterable`, so it meets the type
requirement is allowed to be assigned to `elements`.
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Issue Time Tracking
-------------------
Worklog Id: (was: 339087)
Time Spent: 18.5h (was: 18h 20m)
> Add type hints to python code
> -----------------------------
>
> Key: BEAM-7746
> URL: https://issues.apache.org/jira/browse/BEAM-7746
> Project: Beam
> Issue Type: New Feature
> Components: sdk-py-core
> Reporter: Chad Dombrova
> Assignee: Chad Dombrova
> Priority: Major
> Time Spent: 18.5h
> Remaining Estimate: 0h
>
> As a developer of the beam source code, I would like the code to use pep484
> type hints so that I can clearly see what types are required, get completion
> in my IDE, and enforce code correctness via a static analyzer like mypy.
> This may be considered a precursor to BEAM-7060
> Work has been started here: [https://github.com/apache/beam/pull/9056]
>
>
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