def __getitem__(self, index):
        """Get a single document or a slice of documents from this cursor.

        Raises :class:`~pymongo.errors.InvalidOperation` if this
        cursor has already been used.

        To get a single document use an integral index, e.g.::

          >>> db.test.find()[50]

        An :class:`IndexError` will be raised if the index is negative
        or greater than the amount of documents in this cursor. Any
        limit previously applied to this cursor will be ignored.

        To get a slice of documents use a slice index, e.g.::

          >>> db.test.find()[20:25]

        This will return this cursor with a limit of ``5`` and skip of
        ``20`` applied.  Using a slice index will override any prior
        limits or skips applied to this cursor (including those
        applied through previous calls to this method). Raises
        :class:`IndexError` when the slice has a step, a negative
        start value, or a stop value less than or equal to the start
        value.

        :Parameters:
          - `index`: An integer or slice index to be applied to this cursor
        """
        self.__check_okay_to_chain()
        self.__empty = False
        if isinstance(index, slice):
            if index.step is not None:
                raise IndexError("Cursor instances do not support slice steps")

            skip = 0
            if index.start is not None:
                if index.start < 0:
                    raise IndexError("Cursor instances do not support"
                                     "negative indices")
                skip = index.start

            if index.stop is not None:
                limit = index.stop - skip
                if limit < 0:
                    raise IndexError("stop index must be greater than start"
                                     "index for slice %r" % index)
                if limit == 0:
                    self.__empty = True
            else:
                limit = 0

            self.__skip = skip
            self.__limit = limit
            return self

        if isinstance(index, (int, long)):
            if index < 0:
                raise IndexError("Cursor instances do not support negative"
                                 "indices")
            clone = self.clone()
            clone.skip(index + self.__skip)
            clone.limit(-1)  # use a hard limit
            for doc in clone:
                return doc
            raise IndexError("no such item for Cursor instance")
        raise TypeError("index %r cannot be applied to Cursor "
                        "instances" % index)
dataset/ETHPy150Open blynch/CloudMemeBackend/pymongo/cursor.py/Cursor.__getitem__/original