python的引用和浅拷贝和p深拷贝

环境：python2.7

import copy

a = [1, 2, 3, 4, 5, [1, 2, 3]]
b = a
c = copy.copy(a)
d = copy.deepcopy(a)
print a
print b
print c
print d
#[1, 2, 3, 4, 5, [1, 2, 3]]
#[1, 2, 3, 4, 5, [1, 2, 3]]
#[1, 2, 3, 4, 5, [1, 2, 3]]
#[1, 2, 3, 4, 5, [1, 2, 3]]

a.append(6)
print a
print b
print c
print d
#[1, 2, 3, 4, 5, [1, 2, 3], 6]
#[1, 2, 3, 4, 5, [1, 2, 3], 6]
#[1, 2, 3, 4, 5, [1, 2, 3]]
#[1, 2, 3, 4, 5, [1, 2, 3]]

a = [1, 2, 3, 4, 5, [1, 2, 3]]
b = a
c = copy.copy(a)
d = copy.deepcopy(a)
a[5].append(6)
print a
print b
print c
print d
#[1, 2, 3, 4, 5, [1, 2, 3, 6]]
#[1, 2, 3, 4, 5, [1, 2, 3, 6]]
#[1, 2, 3, 4, 5, [1, 2, 3, 6]]
#[1, 2, 3, 4, 5, [1, 2, 3]]

b是a的引用，a若改变b会随之改变；
c是a的浅拷贝，a内部对象若改变c不会随之改变，但a内部对象的子对象若改变，c会随之改变

d是a的深拷贝，a怎么改变d都不会改变