通过创建tuplles的排序列表在python中对字典进行排序不起作用

Question

I've been using the solution provided in Sorting_Dictionary to sort a dictionary according to values.I know dictionaries cannot be as such sorted but a list of sorted tupples can be obtained.

Complete code:

import sys
import pprint


def helper(filename):
    Word_count={}
    f=open(filename)
    for line in f:
        words=line.split()
        for word in words:
            word=word.lower()
            Word_count.setdefault(word,0)
            Word_count[word]+=1
    f.close()
    return Word_count

def print_words(filename):
    Word_count_new=helper(filename)
    sorted_count=sorted(Word_count_new.items(),key=Word_count_new.get,reverse=True)
    for word in sorted_count:
      pprint.pprint(word)

def print_top(filename):
    word_list=[]
    Word_count=helper(filename)
    word_list=[(k,v) for k,v in Word_count.items()]
    for i in range(20):
        print word_list[i] + '\n'
###

# This basic command line argument parsing code is provided and
# calls the print_words() and print_top() functions which you must define.
def main():
  if len(sys.argv) != 3:
    print 'usage: ./wordcount.py {--count | --topcount} file'
    sys.exit(1)

  option = sys.argv[1]
  filename = sys.argv[2]
  if option == '--count':
    print_words(filename)
  elif option == '--topcount':
    print_top(filename)
  else:
    print 'unknown option: ' + option
    sys.exit(1)

if __name__ == '__main__':
  main()

This function produces problem:

def print_words(filename):
    Word_count_new=helper(filename)
    sorted_count=sorted(Word_count_new.items(),key=Word_count_new.get,reverse=True)
    for word in sorted_count:
        pprint.pprint(word)

here helper is a method which returns a dictionary which is to be sorted. The dictionary is like this {Dad:1, Mom:2, baby:3}

But this doesn't produce a sorted list of tupples. Instead the output is somewhat random like this

('he', 111)
("hot-tempered,'", 1)
('made', 29)
('wise', 2)
('whether', 11)
('wish', 21)
('scroll', 1)
('eyes;', 1)
('this,', 17)
('signed', 2)
('this.', 1)

How can we explain this behaviour?

Answer 1

 sorted_count = sorted(Word_count_new.items(), key=lambda x: x[1], reverse=True)

According to the documentation for sorted ( https://docs.python.org/3/library/functions.html#sorted ), the second argument is a function that creates a comparison key from each list element , so not the dict as a whole.

Word_count_new.items() returns an iterable (in python3, list in python2) of tuples, which is what's passed to your key function. If you want your comparison key to be based of the work frequency (the second element), you want to return the second element in this function ( x[1] where x is the individual tuple getting compared).

To also explain the random output you got, your key was Word_count_new.get . Since your dict does not have tuples as keys, the default value will be None.