How to analyse text and count word frequencies in python

count_words.py

import re
import string

frequency = {}
document_text = open('test.txt', 'r')
text_string = document_text.read().lower()
match_pattern = re.findall(r'\b[a-z]{3,15}\b', text_string)

for word in match_pattern:
    count = frequency.get(word,0)
    frequency[word] = count + 1

frequency_list = frequency.keys()

results = {}
for words in frequency_list:
     results[words] = frequency[words]

# print results.items()

print sorted(results.items(), key=lambda x: x[1])