python中函数使用全局变量方法：加global

common_words = obama_words.sort('count', ascending=False)['word'][:5]
common_words = set(common_words)
count = 0

def has_top_words(word_count_vector):
    # extract the keys of word_count_vector and convert it to a set
    unique_words = word_count_vector.keys()
    unique_words = set(unique_words)
    
    returnWord = common_words.issubset(unique_words)
    
    global count
    if returnWord == True:
        count = count + 1

    # return True if common_words is a subset of unique_words
    # return False otherwise
    return returnWord

wiki['has_top_words'] = wiki['word_count'].apply(has_top_words)
print(count)

上述代码中，函数has_top_words需要用到count这个全局变量，定义在函数之外，函数中使用前，需要在count前加 global。

代码运行后如下：