遍历有序字典中的最后x个元素？

Question

I want to go through an x number of the most recently added entries of an ordered dictionary. So far, the only way I can think of is this:

listLastKeys = orderedDict.keys()[-x:]
for key in listLastKeys:
    #do stuff with orderedDict[key]

But it feels redundant and somewhat wasteful to make another list and go through the ordered dictionary with that list when the ordered dictionary should already know what order it is in. Is there an alternative way? Thanks!

Answer 1

Iterate over the dict in reverse and apply an itertools.islice :

from itertools import islice

for key in islice(reversed(your_ordered_dict), 5):
    # do something with last 5 keys

Answer 2

Instead of reversing it like you are, you can loop through it in reverse order using reversed() . Example:

D = {0 : 'h', 1: 'i', 2:'j'}

x = 1
for key in reversed(D.keys()):
    if x == key:
        break

Answer 3

You could keep a list of the keys present in the dictionary last run.

I don't know the exact semantics of your program, but this is a function that will check for new keys.

keys=[] #this list should be global

def checkNewKeys(myDict):
    for key, item in myDict.iteritems():
        if key not in keys:
            #do what you want with new keys
            keys.append(key)

This basically keep track of what was in the dictionary the whole run of your program, without needing to create a new list every time.