Functions, by default, return None if they come to the end of themselves without returning. So, since there are no return statements in func, it will return None when called.
Furthermore, by using print func(my_list), you are telling Python to print what is returned by func, which is None.
To fix your problem, just drop the print and do:
func(my_list)
Also, if my_list isn't very long, then you don't really need a function at all to do what you are doing. Just use the join method of a string like so:
>>> my_list = ['a','b','c']
>>> print "\n".join(my_list)
a
b
c
>>>
