Python list append and + difference analysis _python

When you use a list in Python, you often need to add an element to a list, like the following two ways to use:

Copy Code code as follows:

t = [1, 2, 3]
T1 = T.append ([4])
t2 = t + [4]

The above two ways of using are different, let's take a look at the actual effect of the operation:

Copy Code code as follows:

>>> t = [1, 2, 3]
>>> T1 = T.append ([4])
>>> T
[1, 2, 3, [4]]
>>> T1
>>>
>>> t2 = t + [4]
>>> T2
[1, 2, 3, [4], 4]
>>> T
[1, 2, 3, [4]]

As you can see Using T.append ([4]), it actually increases in the list of T, not what we expect to increase in T1, and T1 to none at this point.

Instead of using t2 = t + [4], T2 adds another element 4 on the basis of the original T1 and the element in the actual list T is unchanged.

Conclusion:

Using append is actually modifying a list, using + is actually creating a new list.