[python] Python NoneType object is not callable (beginner)

You want to pass the function object hi to your loop() function, not the result of a call to hi() (which is None since hi() doesn't return anything).

So try this:

>>> loop(hi, 5)
hi
hi
hi
hi
hi

Perhaps this will help you understand better:

>>> print hi()
hi
None
>>> print hi
<function hi at 0x0000000002422648>