Indexing and Slicing: __getitem__ and __setitem__ methods allow your classes to mimic some of the behaviors of sequences and mappings.
If defined in a class (or inherited by it), the __getitem__ method is called automatically for instance-indexing operations.
When an instance X appears in an indexing expression like X[i], Python calls the __getitem__ method inherited by the instance, passing X to the first argument and the index in brackets to the second argument.
class Indexer: def __getitem__(self, index): return index ** 2 X = Indexer() # w w w.j ava 2 s . com X # X[i] calls X.__getitem__(i) for i in range(5): print(X[i], end=' ') # Runs __getitem__(X, i) each time