Missing word

[espinoza]

The negative expression would be "keep going until that doesn't happen" if this refers to the while condition.

[AllenDowney]

I think this sentence is correct as written. It might be confusing because the reformulated condition isn't explicitly negative, except for the use of "until". I'll think about how to rephrase.

[AllenDowney]

Thanks for reporting this, and thanks for reading Think Python.

I should note that I’m no longer maintaining the second edition, so I’m generally not making additional corrections or updates there.

The third edition is the current version and is actively maintained:

https://allendowney.github.io/ThinkPython/

If you switch to the third edition and still encounter a problem, feel free to open an issue there.