Is the official documentation on Python.org wrong, or did I interpret something wrongly? Near the end of the Lists Section of the documentation in "An Informal Introduction to Python", one can find the following description about copying lists: Simple assignment in Python never copies data. When you assign a list to a variable, the variable refers to the existing list. Any changes you make to the list through one variable will be seen through all other variables that refer to it.: >>> rgb = ["Red", "Green", "Blue"] >>> rgba = rgb >>> id(rgb) == id(rgba) # they reference the same object True >>> rgba.append("Alph") >>> rgb ["Red", "Green", "Blue", "Alph"] So I understand that the new list is a reference to the original list. But immediately then, the documentation states: All slice operations return a new list containing the requested elements. This means that the following slice returns a shallow copy of the list: >>> correct_rgba = rgba[:] >>> correct_rgba[-1] = "Alpha" >>> correct_rgba ["Red", "Green", "Blue", "Alpha"] >>> rgba ["Red", "Green", "Blue", "Alph"] So, if I understand correctly: rgba[:] is the slice operation this makes a shallow copy of the original list it copies data from the original, into a new list that isn't a reference to the original But: after reading about the difference between shallow and deep copies, I understand that shallow copies are references to their original, whilst deep copies are independent (unreferenced) copies in the example above, the documentation creates a deep copy but mentions it as a shallow copy? Continue reading...
