python copy of the list six methods

The following is a list of six kinds of copy mode, in conclusion, there are three principles at the time of reproduction, which $l1$ a, $l6$ is the second, the third part of the other four methods.

import copy
l = [1, 2, [3, 4]]
l1 = l
l2 = l.copy()
l3 = l[:]
l4 = list(l)
l5 = copy.copy(l)
l6 = copy.deepcopy(l)

We can start to print their addresses:

print(id(l))
print(id(l1))
print(id(l2))
print(id(l3))
print(id(l4))
print(id(l5))
print(id(l6))

2515754890952
2515754890952
2515754891912
2515754910792
2515754891208
2515754863048
2515754910984

It can be seen, $l1$ replication principle is to $l$ The address also be copied later, that is, when $l$ When changed, $l1$ will change. But other means of copying this problem does not occur, such as:

l[0] = 0
print('l: ', l)
print('l1: ', l1)
print('l2: ', l2)
print('l3: ', l3)
print('l4: ', l4)
print('l5: ', l5)
print('l6: ', l6)

get:

l:  [0, 2, [3, 4]]
l1:  [0, 2, [3, 4]]
l2:  [1, 2, [3, 4]]
l3:  [1, 2, [3, 4]]
l4:  [1, 2, [3, 4]]
l5:  [1, 2, [3, 4]]
l6:  [1, 2, [3, 4]]

But if we for $l$ When changes are made to the internal sub-list, only $l6$ will remain the same, such as:

import copy
l = [1, 2, [3, 4]]
l1 = l
l2 = l.copy()
l3 = l[:]
l4 = list(l)
l5 = copy.copy(l)
l6 = copy.deepcopy(l)
l[2][0] = 0
print('l: ', l)
print('l1: ', l1)
print('l2: ', l2)
print('l3: ', l3)
print('l4: ', l4)
print('l5: ', l5)
print('l6: ', l6)

l:  [1, 2, [0, 4]]
l1:  [1, 2, [0, 4]]
l2:  [1, 2, [0, 4]]
l3:  [1, 2, [0, 4]]
l4:  [1, 2, [0, 4]]
l5:  [1, 2, [0, 4]]
l6:  [1, 2, [3, 4]]

So, conclusion:

• $l1 = l$ : When $l$ When changes $l1$ will change.
• $l2 = l.copy()$、 $l3 = l [:]$、 $l4 = list(l)$、 $l5 = copy.copy(l)$：当 $l$ when a single change in the number, $l2$ , $l3$ , $l4$ , $l5$ does not change; when $l$ sublist changes, $l2$ , $l3$ , $l4$ , $l5$ will change.
• $l6 = copy.deepcopy(l)$ : Whether $l$ how change, $l6$ do not change.