Implementation of the list in Python subtraction operation introduction _python

Question Description: Suppose I have such two list,

One is list1,list1 = [1, 2, 3, 4, 5]
One is list2,list2 = [1, 4, 5]
How do we get a new list,list3,
The LIST3 includes all elements in the list1 that are not present in the List2.
namely: List3 = List1–list2

Solution:We can use the set (set) operation
LIST3 = List (set (List1) –set (LIST2))

The set operation converts a list into a collection.
Hypothesis: list_t = [1, 2, 3, 1]
So: List (set (list_t)) = [1, 2, 3]
Yes, duplicate items will be deleted.

Other scenarios:list3 = [I for I-list1 if I not in List2] #可用于list分片
This is also very intuitive to write.
But when the list is large, there is no set method fast.

Extra Knowledge:a = [[I,j] for I in range (2) for J in Range (3)]
This is very similar to "other schemes",
are judged and calculated in [].
Feel very convenient, at least more convenient, faster than the following:
A = []
For I in range (2):
For j in Range (3):
A.append ([i,j])

Some questions: if list_tmp = [[1,2],[2,3]]
The list is not composed of individual elements, but list,
Then set (LIST_TMP) will go wrong.

also to study:hash function