如何按降序打印频率？

我已经看过其他类似的问题，但无法将答案应用到我的程序中。目前频率按升序打印，我该如何更改才能使其按降序打印？

from sys import argv
frequencies = {}
for ch in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
   frequencies[ch] = 0

for filename in argv[1:]:
    try:
        f = open(filename)
    except IOError:
        print 'skipping unopenable', filename
        continue

 text = f.read()                
 f.close()                      

 for ch in text:                
     if ch.isalpha():
         ch = ch.upper()
         frequencies[ch] = frequencies[ch] + 1

for ch in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
    print ch, frequencies[ch]

提前致谢。

您不必重新发明轮子。使用标准库功能：

from sys import argv
from collections import Counter

frequencies = Counter()

for filename in argv[1:]:
    with open(filename) as f:
        text = f.read()
    frequencies.update(ch.upper() for ch in text if ch.isalpha())

for ch, freq in frequencies.most_common():
    print ch, freq