When we say JVM code is not efficient in terms of FLOPs we&#x27;re talking about a factor of 2 or so though, not really the same as the factor of 20+ you lose by implementing numeric code in pure Python. So Scala gives you a 10x faster cycle during early development. Maybe it&#x27;s fast enough that you don&#x27;t need that last factor of 2, or maybe just JNIing a few core operations is enough (you can also do some tricks with the advanced type system; with NumPy if it looks like Python iteration then it is, whereas with something like Breeze you can potentially have something that looks like Scala iteration but won&#x27;t actually copy the data back and forth). But in the cases where you do need to push things right down into Fortran, Scala is just as good a glue language as Python is.