In Julia this would read using broadcasting:

    X = ones(Int, 1_000_000_000)
    Y = ones(Int, 1_000_000_000)

    # explicit dot notation
    X .+= 2 .* Y

    # or with a macro
    @. X += 2 * Y

The + and * do not allocate, the operations are fused into element-wise operations so the vectors are traversed only once, and the loop is compiled to vectorized code. No need for Numpy / BLAS.