> Why not use a statically typed language for such a large code-base? Is this done by purpose, or did they end up with a million lines of Python code and are lo

> Why not use a statically typed language for such a large code-base? Is this done by purpose, or did they end up with a million lines of Python code and are looking for ways to make the maintenance easier? Being in a similar (though much smaller scale) situation ourselves, I suspect your latter suggestion is the answer; they wound up with a large amount of Python code due to expediency (Python is good at quickly getting things done), and are now finding the code base quite hard to maintain. Something to remember is that as of 10 years ago, statically typed languages consisted of C (for some definition of "statically typed"), C++ (complicated and cumbersome, and didn't yet have widespread availability of "modern" C++ features), Java (cumbersome, heavyweight, lots of missing opportunities for abstraction back then), C# (heavily tied into the Microsoft ecosystem, not yet open source), and a bunch of weird academic languages that required tutorials about burritos to learn (ML, Haskell, etc). While statically typed languages like C, C++, and Java were the mainstream languages of the 90s, C was too limited for a lot of people, C++ and Java too cumbersome to use, and so lightweight dynamically typed languages like Perl, Python, PHP, Ruby, and JavaScript picked up a lot of steam due to how much easier to pick up and more productive many programmers found themselves in those languages. But now we have large, fairly un-maintainable code bases in these languages, and people are realizing the value of static typing, in part due to the maintenance hassle and in part due to newer, more expressive and accessible statically typed languages being available (Elm, Rust, TypeScript, Scala, Go, Kotlin, as well as improvements to C++, Java, and C#). But that leaves all of these old codebases, that are hard to maintain. Rather than doing a complete rewrite, adding static typing capabilities that can be applied to existing codebases is a way to make them more maintainable without spending all of the time of a complete rewrite and having everyone have to spend all of the time learning the new language while still maintaining the old codebase.