Print class that uses __getitem__ in python as list
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I have a class that should act as a list of differences (deltas), as calculated from another list. For example, if I have a list of positions, I can use my class to have a dynamically created list of displacements.

For that, I've used the `__getitem__` method the following way:
    
    class Deltas(object):
        def __init__(self, ref):
            self.ref = ref
        
        def __getitem__(self, index):
            if index == 0:
                return 0
            else:
                return self.ref[index] - self.ref[index-1]
                
    samplelist = [1,2,3,5,7,9]
    
    deltas = Deltas(samplelist)

If I print individual elements, it works fine, but if I print the whole list, it gives me:
    
    > print deltas
    <__main__.Deltas object at 0x7f7aa93e3b50>

I'd like to know what other method I have to implement to get this:

    > print deltas
    [0, 1, 1, 2, 2, 2]