[GitHub] [beam] aaronsarna commented on issue #24704: [Feature Request]: Support TypeDict hint in Apache Beam.

["aaronsarna (via GitHub)" <gi...@apache.org>]

aaronsarna commented on issue #24704:
URL: https://github.com/apache/beam/issues/24704#issuecomment-1647981271

   The value of TypedDict over Mapping is if the different keys are expected to have different values. For example, let's say I did the following:
   ```
    to_group = {
     'ints': pcoll1,  # PCollection of (str, int)
     'strs': pcoll2,  # PCollection of (str, str)
   }
   grouped = to_group | beam.CoGroupByKey()
   something = grouped | beam.MapTuple(map_grouped)
   ```
   
   If using Mapping, the method would have to start:
   ```
   def map_grouped(key: str, values: Mapping[str, Iterable[str | int]]):
     ints = values['ints']  # type: Iterable[int]
     strs = values['strs']  # type: Iterable[str]
     ...
   ```
   since the type checker can't tell which key corresponds with which value type.
   
   If I could instead have a TypedDict, it could be a bit cleaner:
   ```
   class GroupedValues(TypedDict):
     ints: Iterable[int]
     strs: Iterable[str]
   
   def map_grouped(key: str, values: GroupedValues):
     ints = values['ints']
     strs = values['strs']
   ```
   and the type checker needs no additional help.


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