修改列表列表中的项目时，也会更改其他列表中相同项目的位置

Question

下面的代码是函数的一部分，但我遇到的问题是在这些行上

# Global variables
NUM_MECS          = 2
MAX_MEC_CAPACITY  = 2
VNF_TYPES         = 2

# Mec capacity to hold a vnf
served_vnfs = list(range(MAX_MEC_CAPACITY+1)) # 0 does not  count as capacity
# All possible mec states as far as holded vnfs
mec_capacity_states = [list(s) for s in itertools.product(served_vnfs, repeat=VNF_TYPES)]
# All possible states with defined number of mecs
mecs_states = [list(p) for p in itertools.product(mec_capacity_states, repeat=NUM_MECS)]

这将生成一个列表列表，如下所示：

out: [[[0, 0], [0, 0]], [[0, 0], [0, 1]], [[0, 0], [0, 2]], [[0, 0], [1, 0]], [[0, 0], [1, 1]], [[0, 0], [1, 2]], [[0, 0], [2, 0]], [[0, 0], [2, 1]], [[0, 0], [2, 2]], [[0, 1], [0, 0]], [[0, 1], [0, 1]], [[0, 1], [0, 2]], [[0, 1], [1, 0]], [[0, 1], [1, 1]], [[0, 1], [1, 2]], [[0, 1], [2, 0]], [[0, 1], [2, 1]], [[0, 1], [2, 2]], [[0, 2], [0, 0]], [[0, 2], [0, 1]], [[0, 2], [0, 2]], [[0, 2], [1, 0]], [[0, 2], [1, 1]], [[0, 2], [1, 2]], [[0, 2], [2, 0]], [[0, 2], [2, 1]], [[0, 2], [2, 2]], [[1, 0], [0, 0]], [[1, 0], [0, 1]], [[1, 0], [0, 2]], [[1, 0], [1, 0]], [[1, 0], [1, 1]], [[1, 0], [1, 2]], [[1, 0], [2, 0]], [[1, 0], [2, 1]], [[1, 0], [2, 2]], [[1, 1], [0, 0]], [[1, 1], [0, 1]], [[1, 1], [0, 2]], [[1, 1], [1, 0]], [[1, 1], [1, 1]], [[1, 1], [1, 2]], [[1, 1], [2, 0]], [[1, 1], [2, 1]], [[1, 1], [2, 2]], [[1, 2], [0, 0]], [[1, 2], [0, 1]], [[1, 2], [0, 2]], [[1, 2], [1, 0]], [[1, 2], [1, 1]], [[1, 2], [1, 2]], [[1, 2], [2, 0]], [[1, 2], [2, 1]], [[1, 2], [2, 2]], [[2, 0], [0, 0]], [[2, 0], [0, 1]], [[2, 0], [0, 2]], [[2, 0], [1, 0]], [[2, 0], [1, 1]], [[2, 0], [1, 2]], [[2, 0], [2, 0]], [[2, 0], [2, 1]], [[2, 0], [2, 2]], [[2, 1], [0, 0]], [[2, 1], [0, 1]], [[2, 1], [0, 2]], [[2, 1], [1, 0]], [[2, 1], [1, 1]], [[2, 1], [1, 2]], [[2, 1], [2, 0]], [[2, 1], [2, 1]], [[2, 1], [2, 2]], [[2, 2], [0, 0]], [[2, 2], [0, 1]], [[2, 2], [0, 2]], [[2, 2], [1, 0]], [[2, 2], [1, 1]], [[2, 2], [1, 2]], [[2, 2], [2, 0]], [[2, 2], [2, 1]], [[2, 2], [2, 2]]]

例如，如果我只想修改第二个列表第二项中的第二个值：

print(mecs_states[1], '-', mecs_states[1][1], '-', mecs_states[1][1][1])

mecs_states[1][1][1] = 'A'

不仅更改所需的值，还将其他值列在同一索引位置

out: [[[0, 0], [0, 0]], [[0, 0], [0, 'A']], [[0, 0], [0, 2]], [[0, 0], [1, 0]], [[0, 0], [1, 1]], [[0, 0], [1, 2]], [[0, 0], [2, 0]], [[0, 0], [2, 1]], [[0, 0], [2, 2]], [[0, 'A'], [0, 0]], [[0, 'A'], [0, 'A']], [[0, 'A'], [0, 2]], [[0, 'A'], [1, 0]], [[0, 'A'], [1, 1]], [[0, 'A'], [1, 2]], [[0, 'A'], [2, 0]], [[0, 'A'], [2, 1]], [[0, 'A'], [2, 2]], [[0, 2], [0, 0]], [[0, 2], [0, 'A']], [[0, 2], [0, 2]], [[0, 2], [1, 0]], [[0, 2], [1, 1]], [[0, 2], [1, 2]], [[0, 2], [2, 0]], [[0, 2], [2, 1]], [[0, 2], [2, 2]], [[1, 0], [0, 0]], [[1, 0], [0, 'A']], [[1, 0], [0, 2]], [[1, 0], [1, 0]], [[1, 0], [1, 1]], [[1, 0], [1, 2]], [[1, 0], [2, 0]], [[1, 0], [2, 1]], [[1, 0], [2, 2]], [[1, 1], [0, 0]], [[1, 1], [0, 'A']], [[1, 1], [0, 2]], [[1, 1], [1, 0]], [[1, 1], [1, 1]], [[1, 1], [1, 2]], [[1, 1], [2, 0]], [[1, 1], [2, 1]], [[1, 1], [2, 2]], [[1, 2], [0, 0]], [[1, 2], [0, 'A']], [[1, 2], [0, 2]], [[1, 2], [1, 0]], [[1, 2], [1, 1]], [[1, 2], [1, 2]], [[1, 2], [2, 0]], [[1, 2], [2, 1]], [[1, 2], [2, 2]], [[2, 0], [0, 0]], [[2, 0], [0, 'A']], [[2, 0], [0, 2]], [[2, 0], [1, 0]], [[2, 0], [1, 1]], [[2, 0], [1, 2]], [[2, 0], [2, 0]], [[2, 0], [2, 1]], [[2, 0], [2, 2]], [[2, 1], [0, 0]], [[2, 1], [0, 'A']], [[2, 1], [0, 2]], [[2, 1], [1, 0]], [[2, 1], [1, 1]], [[2, 1], [1, 2]], [[2, 1], [2, 0]], [[2, 1], [2, 1]], [[2, 1], [2, 2]], [[2, 2], [0, 0]], [[2, 2], [0, 'A']], [[2, 2], [0, 2]], [[2, 2], [1, 0]], [[2, 2], [1, 1]], [[2, 2], [1, 2]], [[2, 2], [2, 0]], [[2, 2], [2, 1]], [[2, 2], [2, 2]]]

我错过了什么？我需要列表中的每个列表都是独立的。我猜原因在于itertools的产品，但我不完全理解为什么

解决办法是什么

Answer 1

使用json进行序列化和反序列化

import json

# Mec capacity to hold a vnf
served_vnfs = list(range(MAX_MEC_CAPACITY + 1))  # 0 does not  count as capacity
# All possible mec states as far as holded vnfs
mec_capacity_states = [list(s) for s in itertools.product(served_vnfs, repeat=VNF_TYPES)]
# All possible states with defined number of mecs
mecs_states = [copy.deepcopy(list(p)) for p in 
itertools.product(mec_capacity_states, repeat=NUM_MECS)]
mecs_states = json.loads(json.dumps(list(mecs_states)))

print(mecs_states)
mecs_states[0][0][0] = 'A'
print(mecs_states)

输出

[[[0, 0], [0, 0]], [[0, 0], [0, 1]], [[0, 0], [0, 2]], [[0, 0], [1, 0]], [[0, 0], [1, 1]], [[0, 0], [1, 2]], [[0, 0], [2, 0]], [[0, 0], [2, 1]], [[0, 0], [2, 2]], [[0, 1], [0, 0]], [[0, 1], [0, 1]], [[0, 1], [0, 2]], [[0, 1], [1, 0]], [[0, 1], [1, 1]], [[0, 1], [1, 2]], [[0, 1], [2, 0]], [[0, 1], [2, 1]], [[0, 1], [2, 2]], [[0, 2], [0, 0]], [[0, 2], [0, 1]], [[0, 2], [0, 2]], [[0, 2], [1, 0]], [[0, 2], [1, 1]], [[0, 2], [1, 2]], [[0, 2], [2, 0]], [[0, 2], [2, 1]], [[0, 2], [2, 2]], [[1, 0], [0, 0]], [[1, 0], [0, 1]], [[1, 0], [0, 2]], [[1, 0], [1, 0]], [[1, 0], [1, 1]], [[1, 0], [1, 2]], [[1, 0], [2, 0]], [[1, 0], [2, 1]], [[1, 0], [2, 2]], [[1, 1], [0, 0]], [[1, 1], [0, 1]], [[1, 1], [0, 2]], [[1, 1], [1, 0]], [[1, 1], [1, 1]], [[1, 1], [1, 2]], [[1, 1], [2, 0]], [[1, 1], [2, 1]], [[1, 1], [2, 2]], [[1, 2], [0, 0]], [[1, 2], [0, 1]], [[1, 2], [0, 2]], [[1, 2], [1, 0]], [[1, 2], [1, 1]], [[1, 2], [1, 2]], [[1, 2], [2, 0]], [[1, 2], [2, 1]], [[1, 2], [2, 2]], [[2, 0], [0, 0]], [[2, 0], [0, 1]], [[2, 0], [0, 2]], [[2, 0], [1, 0]], [[2, 0], [1, 1]], [[2, 0], [1, 2]], [[2, 0], [2, 0]], [[2, 0], [2, 1]], [[2, 0], [2, 2]], [[2, 1], [0, 0]], [[2, 1], [0, 1]], [[2, 1], [0, 2]], [[2, 1], [1, 0]], [[2, 1], [1, 1]], [[2, 1], [1, 2]], [[2, 1], [2, 0]], [[2, 1], [2, 1]], [[2, 1], [2, 2]], [[2, 2], [0, 0]], [[2, 2], [0, 1]], [[2, 2], [0, 2]], [[2, 2], [1, 0]], [[2, 2], [1, 1]], [[2, 2], [1, 2]], [[2, 2], [2, 0]], [[2, 2], [2, 1]], [[2, 2], [2, 2]]]

[[['A', 0], [0, 0]], [[0, 0], [0, 1]], [[0, 0], [0, 2]], [[0, 0], [1, 0]], [[0, 0], [1, 1]], [[0, 0], [1, 2]], [[0, 0], [2, 0]], [[0, 0], [2, 1]], [[0, 0], [2, 2]], [[0, 1], [0, 0]], [[0, 1], [0, 1]], [[0, 1], [0, 2]], [[0, 1], [1, 0]], [[0, 1], [1, 1]], [[0, 1], [1, 2]], [[0, 1], [2, 0]], [[0, 1], [2, 1]], [[0, 1], [2, 2]], [[0, 2], [0, 0]], [[0, 2], [0, 1]], [[0, 2], [0, 2]], [[0, 2], [1, 0]], [[0, 2], [1, 1]], [[0, 2], [1, 2]], [[0, 2], [2, 0]], [[0, 2], [2, 1]], [[0, 2], [2, 2]], [[1, 0], [0, 0]], [[1, 0], [0, 1]], [[1, 0], [0, 2]], [[1, 0], [1, 0]], [[1, 0], [1, 1]], [[1, 0], [1, 2]], [[1, 0], [2, 0]], [[1, 0], [2, 1]], [[1, 0], [2, 2]], [[1, 1], [0, 0]], [[1, 1], [0, 1]], [[1, 1], [0, 2]], [[1, 1], [1, 0]], [[1, 1], [1, 1]], [[1, 1], [1, 2]], [[1, 1], [2, 0]], [[1, 1], [2, 1]], [[1, 1], [2, 2]], [[1, 2], [0, 0]], [[1, 2], [0, 1]], [[1, 2], [0, 2]], [[1, 2], [1, 0]], [[1, 2], [1, 1]], [[1, 2], [1, 2]], [[1, 2], [2, 0]], [[1, 2], [2, 1]], [[1, 2], [2, 2]], [[2, 0], [0, 0]], [[2, 0], [0, 1]], [[2, 0], [0, 2]], [[2, 0], [1, 0]], [[2, 0], [1, 1]], [[2, 0], [1, 2]], [[2, 0], [2, 0]], [[2, 0], [2, 1]], [[2, 0], [2, 2]], [[2, 1], [0, 0]], [[2, 1], [0, 1]], [[2, 1], [0, 2]], [[2, 1], [1, 0]], [[2, 1], [1, 1]], [[2, 1], [1, 2]], [[2, 1], [2, 0]], [[2, 1], [2, 1]], [[2, 1], [2, 2]], [[2, 2], [0, 0]], [[2, 2], [0, 1]], [[2, 2], [0, 2]], [[2, 2], [1, 0]], [[2, 2], [1, 1]], [[2, 2], [1, 2]], [[2, 2], [2, 0]], [[2, 2], [2, 1]], [[2, 2], [2, 2]]]

Answer 2

当您构建mecs_states列表时，您不是在创建新的内部列表，而是在引用您在mec_capacity_states中创建的相同的列表。作为一个较小的例子：

import itertools

nums = [1, 2]

pairs = [list(p) for p in itertools.product(nums, repeat=2)]
# pairs = [[1, 1], [1, 2], [2, 1], [2, 2]]
a, b, c, d = pairs  # unpacking 'pairs' for the example later.

nested = [list(p) for p in itertools.product(pairs, repeat=2)]
# nested = [
#     [[1, 1], [1, 1]],
#     [[1, 1], [1, 2]],
#     [[1, 1], [2, 1]],
#     [[1, 1], [2, 2]],
# ...]

关于nested的内部元素的事情是，它们是相同的列表，通过引用，作为pairs的元素：

nested[0][0] is a
# True
nested[0][1] is a
# True

nested[0][0][0] = 'x'
# a = ['x', 1]
# nested = [
#     [['x', 1], ['x', 1]],
#     [['x', 1], ['x', 2]],
#     [['x', 1], [2, 1]],
#     [['x', 1], [2, 2]],
# ...]

因此，当您修改nested[0][0][0]时，即修改nested[0][0]和a都指向的列表。本质上，这是一个稍微复杂一点的问题，人们在做[[]] * 10时会遇到这个问题，所有十个列表在内存中都是相同的列表

您可以通过等到最后，在构建集合之后，将itertools.product提供给您的tuple转换为list来解决这个问题。但是，一旦进入嵌套集合的深度超过了两个级别，就应该开始考虑类或其他数据结构是否更适合封装所需的行为

Answer 3

只需“克隆”一下mecs_states列表项。请参见代码中的copy.deepcopy

import itertools
import copy

NUM_MECS = 2
MAX_MEC_CAPACITY = 2
VNF_TYPES = 2

# Mec capacity to hold a vnf
served_vnfs = list(range(MAX_MEC_CAPACITY + 1))  # 0 does not  count as capacity
# All possible mec states as far as holded vnfs
mec_capacity_states = [list(s) for s in itertools.product(served_vnfs, repeat=VNF_TYPES)]
# All possible states with defined number of mecs
mecs_states = [copy.deepcopy(list(p)) for p in itertools.product(mec_capacity_states, repeat=NUM_MECS)]
print(mecs_states)
print(mecs_states[1], '-', mecs_states[1][1], '-', mecs_states[1][1][1])
mecs_states[1][1][1] = 'A'
print(mecs_states)

输出

[[[0, 0], [0, 0]], [[0, 0], [0, 1]], [[0, 0], [0, 2]], [[0, 0], [1, 0]], [[0, 0], [1, 1]], [[0, 0], [1, 2]], [[0, 0], [2, 0]], [[0, 0], [2, 1]], [[0, 0], [2, 2]], [[0, 1], [0, 0]], [[0, 1], [0, 1]], [[0, 1], [0, 2]], [[0, 1], [1, 0]], [[0, 1], [1, 1]], [[0, 1], [1, 2]], [[0, 1], [2, 0]], [[0, 1], [2, 1]], [[0, 1], [2, 2]], [[0, 2], [0, 0]], [[0, 2], [0, 1]], [[0, 2], [0, 2]], [[0, 2], [1, 0]], [[0, 2], [1, 1]], [[0, 2], [1, 2]], [[0, 2], [2, 0]], [[0, 2], [2, 1]], [[0, 2], [2, 2]], [[1, 0], [0, 0]], [[1, 0], [0, 1]], [[1, 0], [0, 2]], [[1, 0], [1, 0]], [[1, 0], [1, 1]], [[1, 0], [1, 2]], [[1, 0], [2, 0]], [[1, 0], [2, 1]], [[1, 0], [2, 2]], [[1, 1], [0, 0]], [[1, 1], [0, 1]], [[1, 1], [0, 2]], [[1, 1], [1, 0]], [[1, 1], [1, 1]], [[1, 1], [1, 2]], [[1, 1], [2, 0]], [[1, 1], [2, 1]], [[1, 1], [2, 2]], [[1, 2], [0, 0]], [[1, 2], [0, 1]], [[1, 2], [0, 2]], [[1, 2], [1, 0]], [[1, 2], [1, 1]], [[1, 2], [1, 2]], [[1, 2], [2, 0]], [[1, 2], [2, 1]], [[1, 2], [2, 2]], [[2, 0], [0, 0]], [[2, 0], [0, 1]], [[2, 0], [0, 2]], [[2, 0], [1, 0]], [[2, 0], [1, 1]], [[2, 0], [1, 2]], [[2, 0], [2, 0]], [[2, 0], [2, 1]], [[2, 0], [2, 2]], [[2, 1], [0, 0]], [[2, 1], [0, 1]], [[2, 1], [0, 2]], [[2, 1], [1, 0]], [[2, 1], [1, 1]], [[2, 1], [1, 2]], [[2, 1], [2, 0]], [[2, 1], [2, 1]], [[2, 1], [2, 2]], [[2, 2], [0, 0]], [[2, 2], [0, 1]], [[2, 2], [0, 2]], [[2, 2], [1, 0]], [[2, 2], [1, 1]], [[2, 2], [1, 2]], [[2, 2], [2, 0]], [[2, 2], [2, 1]], [[2, 2], [2, 2]]]
[[0, 0], [0, 1]] - [0, 1] - 1
[[[0, 0], [0, 0]], [[0, 0], [0, 'A']], [[0, 0], [0, 2]], [[0, 0], [1, 0]], [[0, 0], [1, 1]], [[0, 0], [1, 2]], [[0, 0], [2, 0]], [[0, 0], [2, 1]], [[0, 0], [2, 2]], [[0, 1], [0, 0]], [[0, 1], [0, 1]], [[0, 1], [0, 2]], [[0, 1], [1, 0]], [[0, 1], [1, 1]], [[0, 1], [1, 2]], [[0, 1], [2, 0]], [[0, 1], [2, 1]], [[0, 1], [2, 2]], [[0, 2], [0, 0]], [[0, 2], [0, 1]], [[0, 2], [0, 2]], [[0, 2], [1, 0]], [[0, 2], [1, 1]], [[0, 2], [1, 2]], [[0, 2], [2, 0]], [[0, 2], [2, 1]], [[0, 2], [2, 2]], [[1, 0], [0, 0]], [[1, 0], [0, 1]], [[1, 0], [0, 2]], [[1, 0], [1, 0]], [[1, 0], [1, 1]], [[1, 0], [1, 2]], [[1, 0], [2, 0]], [[1, 0], [2, 1]], [[1, 0], [2, 2]], [[1, 1], [0, 0]], [[1, 1], [0, 1]], [[1, 1], [0, 2]], [[1, 1], [1, 0]], [[1, 1], [1, 1]], [[1, 1], [1, 2]], [[1, 1], [2, 0]], [[1, 1], [2, 1]], [[1, 1], [2, 2]], [[1, 2], [0, 0]], [[1, 2], [0, 1]], [[1, 2], [0, 2]], [[1, 2], [1, 0]], [[1, 2], [1, 1]], [[1, 2], [1, 2]], [[1, 2], [2, 0]], [[1, 2], [2, 1]], [[1, 2], [2, 2]], [[2, 0], [0, 0]], [[2, 0], [0, 1]], [[2, 0], [0, 2]], [[2, 0], [1, 0]], [[2, 0], [1, 1]], [[2, 0], [1, 2]], [[2, 0], [2, 0]], [[2, 0], [2, 1]], [[2, 0], [2, 2]], [[2, 1], [0, 0]], [[2, 1], [0, 1]], [[2, 1], [0, 2]], [[2, 1], [1, 0]], [[2, 1], [1, 1]], [[2, 1], [1, 2]], [[2, 1], [2, 0]], [[2, 1], [2, 1]], [[2, 1], [2, 2]], [[2, 2], [0, 0]], [[2, 2], [0, 1]], [[2, 2], [0, 2]], [[2, 2], [1, 0]], [[2, 2], [1, 1]], [[2, 2], [1, 2]], [[2, 2], [2, 0]], [[2, 2], [2, 1]], [[2, 2], [2, 2]]]