I using Python3 but I don’t think this question is specific to Python3

CODE

i = 1
g = 'AABBCCDD'
a = 'A'
print('g[:i] + a + g[i+1:] = ' + g[:i] + a + g[i+1:])
m = g[:i] + a + g[i+1:]
print('m = ' + m)

OUTPUT

g[:i] + a + g[i+1:] = AABBCCDD
m = AAABBCCDD

CODE

i = 6
g = 'AABBCCDD'
a = 'C'
print('g[:i] + a + g[i+1:] = ' + g[:i] + a + g[i+1:])
m = g[:i] + a + g[i+1:]
print('m = ' + m)

OUTPUT

g[:i] + a + g[i+1:] = AABBCCDD
m = AABBCCCDD

What could be the explanation ?