I can't understand this problem

[ichabod801]

The first answer is a little tricky. Lists are mutable types. One consequence of this is that if you modify a list you passed to a function, the list outside will be modified also. But you didn't modify the list. You reassigned the variable name of the parameter to a new list. The variable name exists only inside the function, and has no affect outside of it.

Note that my_list + [4, 5] is almost the same as my_list.extend([4, 5]). The difference is that the addition creates a new list you can reassign, while the second modifies the original list in place.

The second question is easier. When you print a function call, you are printing the return value of that function. Since you didn't specify a return value with a return statement, you get the default return value of None. If you had ended your function with return my_list, printing the function call would have printed the modified list.