I want to substract a number from an array in python but I want to keep the original array.

Here's my code:

```
for X0 in [X0 * 0.01 for X0 in range(-2,2)]:
    for Y0 in [Y0 * 0.01 for Y0 in range(6,10)]:
        RAm = RA
        Decm = Dec
        RAm[:] = [x - X0 for x in RAm]
        Decm[:] = [x - Y0 for x in Decm]
        RAs = np.sum(RAm)
        Decs = np.sum(Decm)
        #a = np.sqrt(((RAs**2*Decs**2)**2 - RAs**4*Decs**4)/(RAs**2*Decs**2*Decs**2 -Decs**2*RAs**4))
        #b = np.sqrt(((RAs**2*Decs**2)**2 - RAs**4*Decs**4)/(RAs**2*Decs**2*RAs**2 - RAs**2*Decs**4))
        print RA
        print RAm

```

This gives me that RA is changing even though it should stay the same because I want to substract a different number from RA each loop. How can I fix this?