How to substitute a entire line for a specific value Python

Question

I have a 4x4 matrix B. I want to substitue the entire first line for a specific value (2):

B[0]=2.0

If I put this way the first line becomes [2,[....],[....],[....]] and not [[2,2,2,2],[....],[....],[....]] .

How can I fix that?

Answer 1

You can do B[0] = [2 for x in range(4)]

you could also do B[0] = [2,2,2,2] but if the size changes then you can put B[0] = [2 for x in range(size)]