I think it is just pure python

I don't know about mojo, but they seem to import python module for this benchmark. https://github.com/modularml/mojo/blob/5ce18c47a27c0c4123de1...

And for some reason they don't compare against NumPy https://github.com/modularml/mojo/blob/5ce18c47a27c0c4123de1...

What would be more interesting is to use NumPy and do the vectorized opreations.