Exception chaining with raise from

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Accepted Answer

The `raise X from Y` syntax sets the __cause__ attribute on X to Y, establishing an explicit exception chain. The outer handler catches RuntimeError, so type(err).__name__ is "RuntimeError". err.__cause__ is the original ValueError, so type(err.__cause__).__name__ is "ValueError". This chaining pattern is important when wrapping low-level library errors into domain-specific ones - you keep the root cause visible without exposing internal details in the exception type itself.