When I use data_copy = data instead of data_copy = data[:], it seems after running the sorting both the original list and copy is getting affected. Can someone help me understand why we are using data[:] for making a copy of the list?

Hey Nirmal, Thank you for the great question! The observation you've made is indeed very important. In Python, when you write data_copy = data you are not making a true copy of the original list. Rather, you are pointing to it. This means that any changes you perform on the data_copy list would affect the data list as well. One way to make a true copy of the original list is through slicing, just as Giles has done: data_copy = data[:] In this way, whatever changes you make on data_copy won't be translated to the data list. The concept of slicing is explained in Section 6: For Loops, Lecture: Lists. A yet another way to make a true copy of the original list is by applying the copy() method as follows: data_copy = data.copy() Again, any changes made on the data_copy list won't affect the data list. Hope this helps! Kind regards, 365 Hristina