如何解决Python列表分块后最后子列表残留单个元素的问题

问题背景 #

要把长度为29的列表OList按指定的DivideLen=12分割成多个子列表，要求最后一个子列表元素数量不足DivideLen时，把它的元素分配到前面的子列表里，再删掉这个最后子列表。但当前代码执行后，最后子列表还剩1个元素没分配完。

原代码 #

# Length of OList is 29
DivideLen = 12
OList = [
    "A", "B", "C", "D", "E",
    "F", "G", "H", "I", "J",
    "K", "L", "M", "N", "O",
    "P", "Q", "R", "S", "T",
    "U", "V", "W", "X", "Y",
    "Z", "AA", "AB", "AC",
]

# Divide OList to multiple small list of length 12
DividedList = [OList[i:i + DivideLen] for i in range(0, len(OList), DivideLen)]

LastIndex = len(DividedList) - 1
LastList = DividedList[LastIndex]

if len(DividedList) > 1 and len(LastList) < DivideLen:
    # Run a Loop from Zero to Less then the Index of Last List of DividedList
    for i in range(0, LastIndex):
        for elem in LastList:
            print(f"Length of List {i} Before: {len(DividedList[i])}")
            print(f"Length of Last List Before: {len(DividedList[LastIndex])}")
            DividedList[i].append(elem)
            DividedList[LastIndex].remove(elem)
            print(f"Length of List {i} After: {len(DividedList[i])}")
            print(f"Length of Last List After: {len(DividedList[LastIndex])}")

当前结果 #

DividedList =[
  [
    "A", "B", "C", "D", "E",
    "F", "G", "H", "I", "J",
    "K", "L", "Y", "Z", "AA",
  ],
  [
    "M", "N", "O", "P", "Q",
    "R", "S", "T", "U", "V",
    "W", "X", "AB"
  ],
  [
     "AC"
  ]
]

预期结果 #

DividedList =[
  [
    "A", "B", "C", "D", "E",
    "F", "G", "H", "I", "J",
    "K", "L", "Y", "Z", "AA",
  ],
  [
    "M", "N", "O", "P", "Q",
    "R", "S", "T", "U", "V",
    "W", "X", "AB", "AC"
  ]
]

问题原因 #

原循环逻辑错误：外层遍历前序子列表，内层遍历剩余元素时，第一个前序子列表会先把剩余元素逐个加完，等轮到第二个前序子列表时，剩余元素已经被改得只剩2个，加完后还剩1个。这种嵌套循环的方式根本不是均匀分配，而是把剩余元素一股脑先塞给第一个子列表，再塞给第二个，逻辑完全不符合需求。

修复方案 #

换一种分配逻辑：轮流把剩余元素分配给前序的每个子列表，直到剩余元素为空，最后删掉空的最后子列表。

修改后的代码片段（替换原有的if块内容）：

if len(DividedList) > 1 and len(LastList) < DivideLen:
    # 循环分配剩余元素，直到最后子列表为空
    while len(LastList) > 0:
        # 轮流给每个前序子列表加元素
        for i in range(LastIndex):
            if not LastList:
                break
            elem = LastList.pop(0)
            DividedList[i].append(elem)
    # 删除空的最后子列表
    del DividedList[LastIndex]

验证结果 #

执行修改后的代码，DividedList会和预期结果完全一致：前两个子列表分别分配到3个和2个剩余元素，最后子列表被删除。

内容的提问来源于stack exchange，提问作者Aly