Python -subtraction of value within a list

Question

I'm new to Python and I'm having difficulties with lists. I wish to subtract 1 from all the values within the list except for values 10.5. The code below gives an error that the x3 list assignment index is out of range. The code so far:

x2=[10.5, -6.36, 11.56, 19.06, -4.37, 26.56, 9.38, -33.12, -8.44, 0.31, -13.44, - 6.25, -13.44, -0.94, -0.94, 19.06, 0.31, -5.94, -13.75, -23.44, -51.68, 10.5]
x3=[]
i=0
while (i<22):
 if x2[i]==10.5:
    x3[i]=x2[i]
else:
    x3[i]=x2[i]-1
break
#The result I want to achieve is:
#x3=[10.5, -7.36, 10.56, 18.06, -5.37, 25.56, 8.38, -34.12, -9.44, -1.31, -14.44, -7.25, -14.44, -1.94, -1.94, 18.06, -1.31, -6.94, -14.75, -24.44, -52.68, 10.5]

Answer 1

Try the following:

x3 = [((x - 1) if x != 10.5 else x) for x in x2]

Answer 2

x2 = [10.5, -6.36, 11.56, 19.06, -4.37, 26.56, 9.38, -33.12, -8.44, 0.31, -13.44, - 6.25, -13.44, -0.94, -0.94, 19.06, 0.31, -5.94, -13.75, -23.44, -51.68, 10.5]
x3 = map(lambda x: x if x == 10.5 else x - 1, x2)

Python being elegant.