Pythonic way to iterate over a collections.Counter() instance in descending order?

You can iterate over c.most_common() to get the items in the desired order. See also the documentation of Counter.most_common().

Example:

>>> c = collections.Counter(a=1, b=999)
>>> c.most_common()
[('b', 999), ('a', 1)]

Here is the example to iterate the Counter in Python collections:

>>>def counterIterator(): 
...  import collections
...  counter = collections.Counter()
...  counter.update(('u1','u1'))
...  counter.update(('u2','u2'))
...  counter.update(('u2','u1'))
...  for ele in counter:
...    print(ele,counter[ele])
>>>counterIterator()
u1 3
u2 3
 

Your problem was solved for just returning descending order but here is how to do it generically. In case someone else comes here from Google here is how I had to solve it. Basically what you have above returns the keys for the dictionary inside collections.Counter(). To get the values you just need to pass the key back to the dictionary like so:

for x in c:
    key = x
    value = c[key]

I had a more specific problem where I had word counts and wanted to filter out the low frequency ones. The trick here is to make a copy of the collections.Counter() or you will get "RuntimeError: dictionary changed size during iteration" when you try to remove them from the dictionary.

for word in words.copy():
    # remove small instance words
    if words[word] <= 3:
        del words[word]