Use generators instead of list comprehension#4768
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To make tasks faster and more memory-efficient. For example (Notification.id.in_(n.id for n in notifications) is twice as fast as a generator than it is as a list comprehension. Generators are also more memory efficient.
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quis
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Mar 10, 2026
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| Notification.query.filter( | ||
| Notification.id.in_([n.id for n in notifications]), | ||
| Notification.id.in_(n.id for n in notifications), |
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The SQLAlchemy source is too convoluted to work out exactly how this will behave but I would be very wary of inadvertent generator exhaustion here.
The documentation says to use a list (although it doesn’t say not to use a generator).
I’d consider carefully:
- how much time/memory this is saving in the overall context of a request/task
- the complexity cost and potential for introducing subtle errors
- how good this function’s test coverage is
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to make tasks faster and more memory-efficient.
For example (Notification.id.in_(n.id for n in notifications) is twice as fast as a generator than it is as a list comprehension.
Generators are also more memory efficient.