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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