PYTHON PROGRAMMING: What happens at back-end when you copy a List to another?

Consider we have a list ABC which has contents as [1,2,3,4] & we copy the list data to another one says XYZ. What we see after copying a list to another is that in case we make changes to XYZ they too get reflected onto ABC. Why does this happen?

 See below, after copying ABC to XYZ I have deleted the 2nd index of XYZ and fetched the XYZ & ABC details. We see the changes made in XYZ too occur in ABC

Let’s see what happens in the backend to get clarification

  • When I store a data in variable ABC it does not actually contain the values but contains a reference to that list.
  • So, when we copy ABC list to XYZ we do not copy the values but the reference link.

  • Hence when we manipulate the data using XYZ list the changes are reflected for ABC as well.
  • So, if you do not want this to happen use list keyword while copying the data.  Example:                XYZ = list (ABC)

  • Now see the below results:

Hope these details provide you a clear picture of what happens at the back-end when we copy lists in Python.


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