Customize Python Slicing, please advise

Question

I have a class that subclasses the list object. Now I need to handle slicing. From everything I read on the intertubes this has to be done using the __getitem__

Answer 1

See this note:

object.__getslice__(self, i, j)

Deprecated since version 2.0: Support slice objects as parameters to the __getitem__() method. (However, built-in types in CPython currently still implement __getslice__(). Therefore, you have to override it in derived classes when implementing slicing.

So, because you subclass list you have to overwrite __getslice__, even though it's deprecated.

I think you should generally avoid subclassing builtins, there are too many weird details. If you just want a class that behaves like a list, there is a ABC to help with that:

from collections import Sequence

class MyList(Sequence):
    def __init__(self, *items):
        self.data = list(items)

    def __len__(self):
        return len(self.data)

    def __getitem__(self, slice):
        return self.data[slice]

s = MyList(1,2,3)
# lots of free methods
print s[1:2], len(s), bool(s), s.count(3), s.index(2), iter(s)