In programming, there are two types of operations: "out of place" operations create a new object, leaving the original object unchanged. "in place" operations modify the original object without creating a new one, and return None explicitly.
A common example of these different concepts is seen in the use of the methods list.sort() and sorted(...). Using list.sort() and attempting to access an element of the list will result in an error.
# WRONG:
unsorted_list = [3, 1, 2]
sorted_list = unsorted_list.sort() # This will be None
print(sorted_list) # Outputs None. Where did the list go?
list_to_sort = [3, 1, 2]
sorted(list_to_sort)
print(list_to_sort) # The list still isn't sorted. Why?To avoid these errors and unexpected results, you should either use an out-of-place operation (sorted(...)) and assign it to a variable or use an in-place operation (list.sort()) without assignment.