python please

Write a function called words_by_frequency that takes a list of words as its only required argument. The function should return a list of (word, count) tuples sorted by count such that the first item in the list is the most frequent item. Items with the same frequency should be in the same order they appear in the original list of words. words_by_frequency should, additionally, take a second parameter that specifies the maximum number of results to return. If n is passed, then only the n most frequent words should be returned. If n is not passed, then all words should be returned in order of frequency