[python-nl] some observations

[Perdaen, D.M.L.]

I am a novice in python and I did some observations that resulted in two questions:
 
Question 1: Why is it that the dictionary 'b' is global over the methods in scrips 1a and 1c and the result of 'print b' is { 'z' : 10 }? I would expect that dictionary 'b' would be created locally in 'subtest' and that it would stay empty in 'def test' just like in 'script 1b'. Can anybody explain the differences?
# 1a
def test():
    b = {}
    subtest(b)
    print b
def subtest(b):
    b['z'] = 10
 
p = test()
 
result: b = { 'z' : 10 }
 
# 1b
def test():
    b = {}
    subtest(b)
    print b
def subtest(b):
    b = {}
    b['z'] = 10
 
p = test()
 
result: b = {}
 
# 1c
def test():
    b = {}
    subtest(b)
    print b
def subtest(b):
    a = b
    a['z'] = 10
 
p = test()
 
result: b = { 'z' : 10 }
 
Question 2: In script 2a list 'b' stays the same as list 'a'. In scrips 2b int 'b' doesn't stay as int 'a'. Can anybody explain these differences? 
 
# 2a
a = [ 1, 2, 3 ]
print a
b = a
print b
print a.pop()
print a
print b
 
result: 
[ 1, 2, 3 ]
[ 1, 2, 3 ]
3
[ 1, 2 ]
[ 1, 2 ]
 
# 2b
a = 1
print a
b = a
print b
a += 1
print a
print b
 
result: 
1
1
2
1