Where should Python backend code catch, translate, or re-raise exceptions?

Places exception handling at meaningful boundaries and preserves causes, tracebacks, client contracts, and retry safety.

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TL;DR

I catch an exception where the current layer can recover, choose an alternative, add meaningful context, or translate it into that layer's contract. If a function cannot improve the outcome, it should normally let the exception propagate. A bare raise inside an exception handler re-raises with the original traceback. raise DomainError(...) from exc translates the abstraction while preserving the explicit cause.

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Failure ownership, specific catching, `raise` versus `raise from`, logging discipline, API translation, and operational judgment.

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Core answer
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Overview
Exceptions should be handled where code can make a real decision, not caught mechanically at every function.
I catch an exception where the current layer can recover, choose an alternative, add meaningful context, or translate it into that layer's contract. If a function cannot improve the outcome, it should normally let the exception propagate. A bare raise inside an exception handler re-raises with the original traceback. raise DomainError(...) from exc translates the abstraction while preserving the explicit cause.
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Stronger answer
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I catch specific exceptions and keep expected validation, conflict, dependency, and programming failures distinct. A repository can translate a driver exception; an API boundary can map a domain failure to a stable response without exposing stack traces or secrets. The layer that finally handles or terminates the operation normally logs once with request or trace context. Context managers or own cleanup rather than broad catches that return a default value.

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Details

Catching Exception in every layer and logging repeatedly.
Using raise exc when preserving the original traceback is intended.
Translating an exception without preserving its cause.
Returning internal exception text to API clients.

Where should Python backend code catch, translate, or re-raise exceptions?

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