Introduction to the list subtraction operation implemented in Python

problem Description: Suppose I have such a list of two,

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.
That is: List3 = List1–list2

Solution: We can operate with set (set)
LIST3 = List (set (List1) –set (LIST2))

The set operation converts a list into a collection.
Hypothesis: list_t = [1, 2, 3, 1]
Then: List (Set (list_t)) = [1, 2, 3]
Yes, duplicate entries are deleted.

Other scenarios:list3 = [I for i in List1 if I is not in List2] #可用于list分片
This is also very intuitive to write.
But when the list is large, no set method is fast.

Additional 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 and 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]]
That is, the list is not composed of individual elements, but lists,
Then set (LIST_TMP) will have a problem.

also to study:hash function

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