Returns the most frequent element in a list.
- Use 
set()to get the unique values inlst. - Use 
max()to find the element that has the most appearances. 
代码实现
def most_frequent(lst):
  return max(set(lst), key = lst.count)
使用样例
most_frequent([1, 2, 1, 2, 3, 2, 1, 4, 2]) #2