如何访问字典中的第一个和最后一个元素? [英] How to access the first and the last elements in a dictionary?
问题描述
发布之前,我已经经历过>访问字典中的任意元素在Python中,但对此我不确定.
Before posting, I have already gone through Access an arbitrary element in a dictionary in Python, butI'm uncertain about this.
我有一个很长的字典,我必须获取它的第一个和最后一个键的值.我可以使用dict[dict.keys()[0]]
和dict[dict.keys()[-1]]
来获取第一个和最后一个元素,但是由于key:value对是以随机形式输出的(如key:value对的位置是随机的),将提供解决方案吗在此链接中始终有效吗?
I have a long dictionary and I've to get the values of its first and last keys. I can use dict[dict.keys()[0]]
and dict[dict.keys()[-1]]
to get the first and last elements, but since the key:value pairs are outputted in a random form(as in the positioning of the key:value pairs is random), will the solution provided in this link always work?
推荐答案
Use an OrderedDict
, because a normal dictionary doesn't preserve the insertion order of its elements when traversing it. Here's how:
# import the right class
from collections import OrderedDict
# create and fill the dictionary
d = OrderedDict()
d['first'] = 1
d['second'] = 2
d['third'] = 3
# retrieve key/value pairs
els = list(d.items()) # explicitly convert to a list, in case it's Python 3.x
# get first inserted element
els[0]
=> ('first', 1)
# get last inserted element
els[-1]
=> ('third', 3)
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