Unbound local error while attempting to reference a list

[molassascookieman]

I have a basic program in which I enter a business' sales, and it can use one of a few functions like finding the top selling store location and similar. Since I am in an intro class, one of these functions is a bubble sort to sort from best selling location to worst selling location, and vice versa.

def sort_hilo():
    n = len(sales)
    e = len(location)
    swapped = True
    while swapped:
        swapped = False
        for i in range(n - 1):
            if sales[i] > sales[i + 1]:
                temp = sales[i]
                sales[i] = sales[i+1]
                sales[i+1] = temp
                swapped = True
                
        for i in range(n - 1):
            if location[i] > location[i + 1]:
                temp = location[i]
                location[i] = location[i+1]
                location[i+1] = temp
                swapped = True
                
        n -= 1
        e-=1
    for i in range(len(sales)):
        location=i+1
        print('Location', location, '$', ('%0.2f'%sales))

both "sales" and "location" in the first few lines are supposed to reference lists that I globally defined in another part of the program.

The problem is, it keeps giving me back the local variable referenced before assignment for the locations list.
"e = len(location)
UnboundLocalError: local variable 'location' referenced before assignment"

But it doesn't give me this error for the sales list! I have no idea how to get it to realize that it is supposed to reference a predefined list instead of a local variable.