6.6) 'sort', copying and 'sorted'

The sort() list method directly sorts the list it is applied on rather than returning a new list. Therefore if you want to keep the original list you have two options:

• You can work on a copy of the list:

>>> planets=["Mercury","Venus","Earth","Mars"]
>>> planets_ordered=planets[:]   # a copy is done with [:]
>>> planets_ordered.sort()       # this will not affect the original list called 'planets'.

Visualise how copying works in action with this Pythontutor.com animation on list copying.
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• You can use the sorted function which takes one list and returns a new list with the same elements sorted in (alphanumeric) order. So in the previous example:

>>> planets=["Mercury","Venus","Earth","Mars"]
>>> planets_ordered=sorted(planets[:])