kamilwu commented on a change in pull request #13048:
URL: https://github.com/apache/beam/pull/13048#discussion_r503332709
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File path: sdks/python/apache_beam/transforms/core.py
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@@ -1970,10 +1985,14 @@ def add_input_types(transform):
return combined
if self.has_defaults:
- combine_fn = (
- self.fn if isinstance(self.fn, CombineFn) else
- CombineFn.from_callable(self.fn))
- default_value = combine_fn.apply([], *self.args, **self.kwargs)
+ combine_fn = copy.copy(
Review comment:
Better protection against potential side effects.
If using default values, `CombineFn.apply` is called at pipeline
construction time. `CombineFn.setup` and `CombineFn.teardown` are called along
with it. The same instance of CombineFn is then serialized and sent to runner.
I think it would be better to perform initial `CombineFn.apply` on a copy, so
that the state of the instance is not polluted.
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