在 Python 中求和非整数 [英] Summing non-integers in Python

问题描述

是否可以在 Python 中取非整数的总和?

我尝试了命令

sum([[1], [2]])

得到[1, 2]，但它给出了错误

回溯(最近一次调用):文件<pyshell#28>"，第 1 行，在 <module> 中.总和([[1], [2]])类型错误:+ 不支持的操作数类型:'int' 和 'list'

我怀疑 sum 试图将 0 添加到列表 [1]，导致失败.我确信有很多技巧可以解决这个限制(将东西包装在一个类中，并手动实现 __radd__)，但是有没有更优雅的方法来做到这一点?

解决方案

看起来你想要这个:

<预><代码>>>>sum([[1],[2]], [])[1, 2]

您是对的，它试图将 0 添加到 [1] 并出现错误.解决方案是给 sum 一个额外的参数，给出起始值，对你来说就是空列表.

不过，正如 gnibbler 所说，sum 不是连接事物的好方法.如果你只想聚合一系列的东西，你可能应该使用 reduce 而不是为了使用 sum 而创建你自己的 __radd__ 函数.这是一个示例(与 sum 具有相同的不良行为):

<预><代码>>>>减少(lambda x，y:x+y，[[1]，[2]])[1, 2]

Is it possible to take the sum of non-integers in Python?

I tried the command

sum([[1], [2]])

to get [1, 2], but it gives the error

Traceback (most recent call last):
  File "<pyshell#28>", line 1, in <module>
    sum([[1], [2]])
TypeError: unsupported operand type(s) for +: 'int' and 'list'

I suspect sum tries to add 0 to the list [1], resulting in failure. I'm sure there are many hacks to work around this limitation (wrapping stuff in a class, and implementing __radd__ manually), but is there a more elegant way to do this?

解决方案

It looks like you want this:

>>> sum([[1],[2]], [])
[1, 2]

You're right that it's trying to add 0 to [1] and getting an error. The solution is to give sum an extra parameter giving the start value, which for you would be the empty list.

Edit: As gnibbler says, though, sum is not a good way to concatenate things. And if you just want to aggregate a sequence of things, you should probably use reduce rather than make your own __radd__ function just to use sum. Here's an example (with the same poor behavior as sum):

>>> reduce(lambda x, y: x+y, [[1],[2]])
[1, 2]

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