map::lower_bound() 等效于 python 的 dict 类? [英] map::lower_bound() equivalent for python's dict class?

问题描述

我正在编写一些代码，要求我获取键的下限(为简单起见，忽略位于集合中最小键下方的键).

I am writing some code that requires me to fetch the lower bound of a key (for simplicity, ignore keys that lie below the smallest key in the collection).

在 C++ 中，使用 std::map(作为最具可比性的数据类型)我会简单地使用 lower_bound() 来返回迭代器.

In C++, using std::map (as the most comparable data type) I would simply use the lower_bound() to return the iterator.

我的 Pythonfoo 不是那么好，但我猜测(如果 Python 还没有这样做的方法)，这将是 lambda 函数的一个很好的用途......

My Pythonfoo is not that great, but I am guessing that (in case Python does not already have a way of doing this), this would be a good use of a lambda function ...

检索给定索引的下界键的 Pythonic 方法是什么?

What is the Pythonic way of retrieving the lower bound key for a given index?

如果问题太抽象，这就是我真正想做的:

In case the question is too abstract, this is what I am actually trying to do:

我有一个按日期索引的 Python 字典.我希望能够使用日期来查找字典，并返回与指定键的下限相关联的值.

I have a Python dict indexed by date. I want to be able to use a date to look up the dict, and return the value associated with the lowerbound of the specified key.

片段如下:

mymap = { datetime.date(2007, 1, 5): 'foo',
          datetime.date(2007, 1, 10): 'foofoo',
          datetime.date(2007, 2, 2): 'foobar',
          datetime.date(2007, 2, 7): 'foobarbar' }

mydate = datetime.date(2007, 1, 7)

# fetch lbound key for mydate from mymap
def mymap_lbound_key(orig):
    pass # return the lbound for the key 

我真的不想遍历键，寻找第一个键 <= 提供的键，除非没有更好的选择...

I don't really want to loop through the keys, looking for the first key <= provided key, unless there is no better alternative ...

推荐答案

Python 的 dict 类没有这个功能；你需要自己写.如果键已经排序，那肯定会很方便，不是吗，所以你可以对它们进行二分搜索并避免对它们进行迭代?在这种情况下，我将查看 blist 包中的 sorteddict 类.http://pypi.python.org/pypi/blist/

Python's dict class doesn't have this functionality; you'd need to write it yourself. It sure would be convenient if the keys were already sorted, wouldn't it, so you could do a binary search on them and avoid iterating over them all? In this vein, I'd have a look at the sorteddict class in the blist package. http://pypi.python.org/pypi/blist/

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