Why am I getting a SyntaxError in line 6?

Question

x = [2, 4]
a = 0
b = a + 1
y = 0
while y <= 4000000:
x[a] + x[b] = y
x.append(y)
a += 1

Answer 1

At line 6 you are assigning a value to a value ,
2+4=0

which obviously won't work

Answer 2

Replace x[a] + x[b] =y with y = x[a] + x[b]