Write a function in Python that takes in a list of numbers and returns the average of the list.
Here is an example implementation for calculating the mean from scratch:

def calculate_mean(numbers):
    sum = 0
    for number in numbers:
        sum += number
    return sum / len(numbers)

In this case, we first create a variable called "sum" which will hold our total value (i.e., sum). We then iterate through each element in the given list and add it to our sum using the "+=" operator. Finally, we divide by the length of the list to get our final result.