O primeiro portão é um portão Hadamard, normalmente representado por
Em seguida, temos um portão CNOT. Isso é normalmente representado por
This is the right size for two qubits, so we don't need to scale using kronecker products. We then have another hadamard gate, which scales the same was as the first. To find the overall matrix for the circuit, then, we multiply them all together:
(if python multiplied correctly =) We would then multiply this by our original qubit state, and get our result.
So basically, you go through each gate one by one, take the base representation, and scale them appropriately using kronecker products with identity matrices. Then you multiply all the matrices together in the order they are applied. Be sure to do this such that if you wrote out the multiplication, the very first gate is on the far right; as arriopolis points out, this is a common mistake. Matrices are not commutative! If you don't know the base representation of a matrix, check first wikipedia's article on quantum gates which has a lot.