Help with assignment

I am having trouble with a homework assignment. The task is to "Write a function called double_it() that takes a list as a parameter. The function should iterate through the list and multiply each numeric element in the original list by 2. Assume that the list only contains numeric (int or float) values. Return of elements that were doubled". I am having trouble though and do not know why. This is the code I have so far.

def main():
user_list = input("Enter a list of only numbers.")...

Help with assignment