使用 Python 对包含“无"的列表求和

2022-01-09 00:00:00 python sum

问题描述

基本上我的问题是说您有一个包含无"的列表，您将如何尝试检索列表的总和.下面是一个我试过的例子，它不起作用，我得到了错误:TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'.谢谢

Basically my question is say you have an list containing 'None' how would you try retrieving the sum of the list. Below is an example I tried which doesn't work and I get the error: TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'. Thanks

def sumImport(self):
    my_list = [[1,2,3,None],[1,2,3],[1,1],[1,1,2,2]]
    k = sum(chain.from_iterable(my_list))
    return k

解决方案

可以使用filter功能

>>> sum(filter(None, [1,2,3,None]))
6

根据评论更新

filter 的典型用法是 filter(func, iterable)，但是将 None 作为第一个参数传递是一种特殊情况，在 Python 文档.引用:

Typically filter usage is filter(func, iterable), but passing None as first argument is a special case, described in Python docs. Quoting:

如果function为None，则假定恒等函数，即iterable中所有为false的元素都被移除.

If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.

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