Why "a = a + a" is not a cyclic structure where as "a.append(a)" is a cyclic structure?

Question

a = [1,2,3]
a = a + [a]
Print(a)
>>> [1,2,3,1,2,3]

a = [1,2,3]
a.append[a]
Print (a)
>>>[1,2,3,[...]]

Answer 1

Because [a] creates another list and add it to a, but a.append(a) appends the same list to itself and it will be cyclic, look at the example:

In [19]: id(a)
Out[19]: 139994593696008

In [20]: id([a])
Out[20]: 139994605200520

Answer 2

because + creates a new object and append just appends to the original object. if you append a list to itself there is a cycle.

>>> a = [12]
>>> id(a)
4337923136
>>> a = a + [a]
>>> id(a)
4338091360
>>> a
[12, [12]]
>>> a.append(a)
>>> id(a)
4338091360
>>> a
[12, [12], [...]]
>>>