How to show decimal point only when it's not a whole number?

You can use floats' is_integer method. It returns True if a float can be represented as an integer (in other words, if it is of the form X.0):

li = [3.5, 2.5, 5.0, 7.0]

print([int(num) if float(num).is_integer() else num for num in li])
>> [3.5, 2.5, 5, 7]

EDIT

After OP added their code:

Instead of using list comprehension like in my original example above, you should use the same logic with your calculated average:

get_numbers = map(float, line[-1])  # assuming line[-1] is a list of numbers
average_numbers = sum(get_numbers) / len(get_numbers)
average = round(average_numbers * 2) / 2
average = int(average) if float(average).is_integer() else average
print average  # this for example will print 3 if the average is 3.0 or
               # the actual float representation.