Sum vector elements homorphically
As far as I know, there are many libraries that use lattices and LWE schemes to implement fully homomorphic Encryptions.

This is a set, Most of them is in C++ and Only one by MSFT is C#, But in all cases you can port the code to python aftor compiling:


HElib in C++
SEAL By MicroSoft C++/C#
Palisade C++
FHEW C/C++
TFHE C++
NFLib C++


Note: The set in no particular order.