Why do equal integers behave differently to equal lists?

Question

This question is more of curiosity than anything else.

I read the implementation details of an int object in Python ( 1 and 2 ), and as far as I can see, Python int is basically a pointer to C to the structure, right?

So, the question basically is what happens in Python internally, so an equal of two intin python does not point to the same instance with equal complex types, such as list, does:

>>> a=5
>>> b=a
>>> print "id a: %s, id b: %s" % (id(a), id(b))
id a: 40802136, id b: 40802136
>>> b+=1
>>> print "a: %s, b: %s" % (a, b)
a: 5, b: 6
>>> print "id a: %s, id b: %s" % (id(a), id(b))
id a: 40802136, id b: 40802112

>>> a=[5]
>>> b=a
>>> print "id a: %s, id b: %s" % (id(a), id(b))
id a: 45930832, id b: 45930832
>>> b.append(1)
>>> print "a: %s, b: %s" % (a, b)
a: [5, 1], b: [5, 1]
>>> print "id a: %s, id b: %s" % (id(a), id(b))
id a: 45930832, id b: 45930832

, id , , . ? , - "" , ? , int ? ( , : - D)

, . !

Answer 1

, , id .

a = 5
b = a
b += 1             # created a new int
print id(a), id(b) # different

a = 5
b = a
b = b + 1          # created a new int
print id(a), id(b) # different

list append, +:

a = [5]
b = a
b = b + [6]        # created a new list
print id(a), id(b) # different

append int s, int , list .

---

-

a = [5]
b = a
b += [1]
print id(a), id(b) # same

, += ( , IMO) , b += [1] b = b + [1] . (. + = ?)