I interpret NSA as National Security Agency and NASA as the National Aeronautics and Space Administration (two agencies within the US Government). However, considering these are two entire agencies, it does not make sense to say that either is 'written in python'. They may use Python, but I know that they also rely heavily on other languages including C, C++, Java, C#, OCaml, and assembly among others.
Someone else asked for a reference and I provided the link in response also in this thread. I am not arguing it's the only language they use but python are languages they use nonetheless
Yelp Python
Quora Python
Youtube Python
Slide Python
NASA Python