子类Python列表以验证新项目 [英] Subclass Python list to Validate New Items

问题描述

我想要一个python列表，该列表在外部将其自身表示为其内部列表项的平均值，但在其他方面则表现为列表.如果添加了不能转换为浮点数的项目，则应提高TypeError.

I want a python list which represents itself externally as an average of its internal list items, but otherwise behaves as a list. It should raise a TypeError if an item is added that can't be cast to a float.

我遇到的问题是提高TypeError.对于通过任何列表方法(例如.append，.extend，+=，按切片设置等)添加的无效项，应将其引发.

The part I'm stuck on is raising TypeError. It should be raised for invalid items added via any list method, like .append, .extend, +=, setting by slice, etc.

是否可以拦截添加到列表中的新项目并对其进行验证?

我尝试重新验证__getattribute__中的整个列表，但是当调用它时，我只能访问列表的旧版本，而且甚至无法调用初始化，例如+=或像mylist[0] = 5这样的切片.

I tried re-validating the whole list in __getattribute__, but when its called I only have access to the old version of the list, plus it doesn't even get called initialization, operators like +=, or for slices like mylist[0] = 5.

有什么想法吗?

推荐答案

继承自 MutableSequence 并实现其所需的方法以及仅属于序列范围之外的任何其他方法，例如

Inherit from MutableSequence and implement the methods it requires as well as any others that fall outside of the scope of Sequences alone -- like the operators here. This will allow you to change the operator manipulations for list-like capabilities while automatically generating iterators and contains capabilities.

如果要检查切片，则需要在__getitem__(和/或__setitem__)方法中执行isinstance(key, slice).请注意，像myList [0]这样的单个索引不是切片请求，而是像myList [:0]这样的单个索引是实际的切片请求.

If you want to check for slices btw you need to do isinstance(key, slice) in your __getitem__ (and/or __setitem__) methods. Note that a single index like myList[0] is not a slice request, but a single index and myList[:0] is an actual slice request.

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