如果索引不存在，则 Python 列表在索引处设置值 [英] Python list set value at index if index does not exist

问题描述

有没有办法、lib 或 python 中的某些东西可以在不存在的索引处设置列表中的值?类似于在列表中创建运行时索引:

Is there a way, lib, or something in python that I can set value in list at an index that does not exist? Something like runtime index creation at list:

l = []
l[3] = 'foo'
# [None, None, None, 'foo']

更进一步，多维列表:

l = []
l[0][2] = 'bar'
# [[None, None, 'bar']]

或者使用现有的:

l = [['xx']]
l[0][1] = 'yy'
# [['xx', 'yy']]

推荐答案

没有内置，但很容易实现:

There isn't a built-in, but it's easy enough to implement:

class FillList(list):
    def __setitem__(self, index, value):
        try:
            super().__setitem__(index, value)
        except IndexError:
            for _ in range(index-len(self)+1):
                self.append(None)
            super().__setitem__(index, value)

或者，如果您需要更改现有的原版列表:

Or, if you need to change existing vanilla lists:

def set_list(l, i, v):
      try:
          l[i] = v
      except IndexError:
          for _ in range(i-len(l)+1):
              l.append(None)
          l[i] = v

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