The GIST to take is this:
Dealing with shallow lists (no sub_lists, just single elements) using "normal assignment" rises a "side effect" when you create a shallow list and then you create a copy of this list using "normal assignment". This "side effect" is when you change any element of the copy list created, because it will automatically change the same elements of the original list. That is when copy comes in handy, as it won't change the original list elements when changing the copy elements.
On the other hand, copy does have a "side effect" as well, when you have a list that has lists in it (sub_lists), and deepcopy solves it. For instance if you create a big list that has nested lists in it (sub_lists), and you create a copy of this big list (the original list). The "side effect" would arise when you modify the sub_lists of the copy list which would automatically modify the sub_lists of the big list. Sometimes (in some projects) you want to keep the big list (your original list) as it is without modification, and all you want is to make a copy of its elements (sub_lists). For that, your solution is to use deepcopy which will take care of this "side effect" and makes a copy without modifying the original content.
复制和深度复制操作的不同行为只涉及复合对象(即:包含其他对象(如列表)的对象)。
下面是这个简单的代码示例中说明的差异:
第一个
让我们通过创建一个原始列表和这个列表的副本来检查copy (shallow)的行为:
import copy
original_list = [1, 2, 3, 4, 5, ['a', 'b']]
copy_list = copy.copy(original_list)
现在，让我们运行一些打印测试，看看原始列表与它的复制列表相比表现如何:
Original_list和copy_list的地址不同
print(hex(id(original_list)), hex(id(copy_list))) # 0x1fb3030 0x1fb3328
original_list和copy_list中的元素有相同的地址
print(hex(id(original_list[1])), hex(id(copy_list[1]))) # 0x537ed440 0x537ed440
original_list和copy_list的Sub_elements有相同的地址
print(hex(id(original_list[5])), hex(id(copy_list[5]))) # 0x1faef08 0x1faef08
修改original_list元素不会修改copy_list元素
original_list.append(6)
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b']]
修改copy_list元素不会修改original_list元素
copy_list.append(7)
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b'], 7]
修改original_list sub_elements会自动修改copy_list sub_elements
original_list[5].append('c')
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b', 'c'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b', 'c'], 7]
修改copy_list sub_elements会自动修改original_list sub_elements
copy_list[5].append('d')
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b', 'c', 'd'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b', 'c', 'd'], 7]
第二个
让我们来检查deepcopy的行为，通过做和copy相同的事情(创建一个原始列表和这个列表的副本):
import copy
original_list = [1, 2, 3, 4, 5, ['a', 'b']]
copy_list = copy.copy(original_list)
现在，让我们运行一些打印测试，看看原始列表与它的复制列表相比表现如何:
import copy
original_list = [1, 2, 3, 4, 5, ['a', 'b']]
copy_list = copy.deepcopy(original_list)
Original_list和copy_list的地址不同
print(hex(id(original_list)), hex(id(copy_list))) # 0x1fb3030 0x1fb3328
original_list和copy_list中的元素有相同的地址
print(hex(id(original_list[1])), hex(id(copy_list[1]))) # 0x537ed440 0x537ed440
original_list和copy_list的Sub_elements有不同的地址
print(hex(id(original_list[5])), hex(id(copy_list[5]))) # 0x24eef08 0x24f3300
修改original_list元素不会修改copy_list元素
original_list.append(6)
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b']]
修改copy_list元素不会修改original_list元素
copy_list.append(7)
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b'], 7]
修改original_list sub_elements不会修改copy_list sub_elements
original_list[5].append('c')
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b', 'c'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b'], 7]
修改copy_list sub_elements不会修改original_list sub_elements
copy_list[5].append('d')
print("original_list is:", original_list) # original_list is: [1, 2, 3, 4, 5, ['a', 'b', 'c', 'd'], 6]
print("copy_list is:", copy_list) # copy_list is: [1, 2, 3, 4, 5, ['a', 'b', 'd'], 7]
