# -*- coding:utf-8 -*-
import io
import re
  
class Counter:
  def __init__(self, path):
    """
    :param path: 文件路径
    """
    self.mapping = dict()
    with io.open(path, encoding="utf-8") as f:
      data = f.read()
      words = [s.lower() for s in re.findall("\w+", data)]
      for word in words:
        self.mapping[word] = self.mapping.get(word, 0) + 1
  
  def most_common(self, n):
    assert n > 0, "n should be large than 0"
    return sorted(self.mapping.items(), key=lambda item: item[1], reverse=True)[:n]
  
if __name__ == '__main__':
  most_common_5 = Counter("importthis.txt").most_common(5)
  for item in most_common_5:
    print(item)

('is', 10)
('better', 8)
('than', 8)
('the', 6)
('to', 5)