新手python问题，求大佬们帮忙

Question

Smart stats
Write a module called stats that contains two functions:

mean - returns the mean of a list (average)

std - returns the sample standard deviation of a list

Requirements

Parameters: data (list)

Both functions must only accept a list input. When something other than a list is passed to the function then the function should immediately end and return None.

Both functions should ignore non-numeric values in the list.