Use union of current context and left side for right side narrowing of binary ops#19249
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JukkaL merged 5 commits intopython:masterfrom Jun 13, 2025
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Diff from mypy_primer, showing the effect of this PR on open source code: discord.py (https://github.com/Rapptz/discord.py)
- discord/activity.py:384: error: Incompatible types in assignment (expression has type "Any | dict[Any, Any]", variable has type "ActivityAssets") [assignment]
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Fixes #12001. Fixes #6898. Fixes #15368. Improves #17790 and #11508.
When encountering
a {and,or} b, we used to useaas primary context forbinference. This results in weird errors whenaandbare completely unrelated, and in many cases return type/assignment type context can do much better. Inferring to union should be harmless in most cases, so use union ofaand current context instead.