Why is my variable 'D8' getting updated in in the second line?

Question

D8 = D7

D7[np.eye(D7.shape[0], D7.shape[1]).astype('bool')] = np.nan

I want to save D7 as D8 before the second line, but running the second line somehow changes D8???

I'm lost as to why this is happening.

I expected D8 to remain the same after the second line, but I am getting NaN along the diagonals in both D7 and D8 when I only want it in D7.

Answer 1

D8 is a reference to D7, not a copy. If you want a true copy of D7, use D8 = D7.copy().

– MattDMo 7 mins ago

Thank you MattDMo!