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Fix exception cause in runapp.py #552

Merged
merged 1 commit into from
Jun 14, 2020
Merged

Fix exception cause in runapp.py #552

merged 1 commit into from
Jun 14, 2020

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cool-RR
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@cool-RR cool-RR commented Jun 12, 2020

I recently went over Matplotlib, Pandas and NumPy, fixing a small mistake in the way that Python 3's exception chaining is used. If you're interested, I can do it here too. I've done it on just one file right now.

The mistake is this: In some parts of the code, an exception is being caught and replaced with a more user-friendly error. In these cases the syntax raise new_error from old_error needs to be used.

Python 3's exception chaining means it shows not only the traceback of the current exception, but that of the original exception (and possibly more.) This is regardless of raise from. The usage of raise from tells Python to put a more accurate message between the tracebacks. Instead of this:

During handling of the above exception, another exception occurred:

You'll get this:

The above exception was the direct cause of the following exception:

The first is inaccurate, because it signifies a bug in the exception-handling code itself, which is a separate situation than wrapping an exception.

Let me know what you think!

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@MSeal MSeal left a comment

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Thanks -- I think it's mostly an improvement. The queue empty pattern here is somewhat of a misleading exception which is why we wrap it. But since python is giving you both anyway, might as well make it clearer about the relationship

@MSeal MSeal merged commit 5afe272 into jupyter:master Jun 14, 2020
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2 participants