Python列表删除项目，即使没有明确告诉

Question

So I had a very unusual problem with deleting elements from lists, I have recreated the problem in a much smaller and easier to understand format. Basically deleting an item from a list will delete the same item from a different list you have previously set equals to the original list outside of the main loop.

a = [1,2,3,4]
b = a

while True:
    print("a:", a)
    print("b:", b)
    c = int(input("delete"))
    del(a[c])
    print("a:", a)
    print("b:", b)
    break

This returns:

a: [1, 2, 3, 4]
b: [1, 2, 3, 4]
delete2 #the "2" is my input
a: [1, 2, 4]
b: [1, 2, 4]
>>> 

I researched and saw a few things about shallow/deep copies, but i'm not too sure about that, if anyone could shed some more light that would be great

Answer 1

This is because a and b are names of the same list (or more formally, references to the same object).

To create a name for a new list make a copy of it:

b = list(a)
# or
b = a[:]

This will create a new list containing the exact same members and is called shallow-copy.

A deep-copy is when you recursively copy the entire structure but it seems like its not needed here.