A third static analyzer for Python! I wonder what this landscape is going to look like in a few years... (There are probably others, but this is the first I'd heard of Pyre, and I'd only known about mypy and pytype up until today - if there are others I'd love to hear about them!)

On a more substantive note, static analysis is one of those things that sounds like you shouldn't even need it but in reality is a surprisingly powerful tool, for the same reason that all code has bugs: humans honestly suck at writing code. (For those of you that have seen Bret Victor's "Inventing on Principle", I feel like static analysis is one of the first steps in getting to the kind of feedback loop he envisions.)

We have all these ideas around how things should work, but so frequently our mental model diverges slightly from what's actually happening (which dynamic typing only makes worse, and NPEs even more so) and that's on top of the mistakes we make (like this one in the JDK, which was caught using ErrorProne, a static analyzer for Java: https://bugs.openjdk.java.net/browse/JDK-8176402).

Also, a fun tidbit about using static analysis to apply automated code fixes: this is basically when you realize you need auto-formatters, because you still want your code to be indented like a sane person would after applying a change like this. (And imagine how much more complex the autoformatter/autofixer have to be when you think about how they have to do things like preserve comments, etc!)