# Buggy code
def _add_datetimelike_methods(cls):
    """
    add in the datetimelike methods (as we may have to override the
    superclass)
    """

    def __add__(self, other):
        from pandas.core.index import Index
        from pandas.core.indexes.timedeltas import TimedeltaIndex
        from pandas.tseries.offsets import DateOffset

        if isinstance(other, TimedeltaIndex):
            return self._add_delta(other)
        elif isinstance(self, TimedeltaIndex) and isinstance(other, Index):
            if hasattr(other, "_add_delta"):
                return other._add_delta(self)
            raise TypeError(
                "cannot add TimedeltaIndex and {typ}".format(typ=type(other))
            )
        elif isinstance(other, (DateOffset, timedelta, np.timedelta64)):
            return self._add_delta(other)
        elif is_integer(other):
            return self.shift(other)
        elif isinstance(other, (Index, datetime, np.datetime64)):
            return self._add_datelike(other)
        else:  # pragma: no cover
            return NotImplemented

    cls.__add__ = __add__
    cls.__radd__ = __add__

    def __sub__(self, other):
        from pandas.core.index import Index
        from pandas.core.indexes.datetimes import DatetimeIndex
        from pandas.core.indexes.timedeltas import TimedeltaIndex
        from pandas.tseries.offsets import DateOffset

        if isinstance(other, TimedeltaIndex):
            return self._add_delta(-other)
        elif isinstance(self, TimedeltaIndex) and isinstance(other, Index):
            if not isinstance(other, TimedeltaIndex):
                raise TypeError(
                    "cannot subtract TimedeltaIndex and {typ}".format(
                        typ=type(other).__name__
                    )
                )
            return self._add_delta(-other)
        elif isinstance(other, DatetimeIndex):
            return self._sub_datelike(other)
        elif isinstance(other, Index):
            raise TypeError(
                "cannot subtract {typ1} and {typ2}".format(
                    typ1=type(self).__name__, typ2=type(other).__name__
                )
            )
        elif isinstance(other, (DateOffset, timedelta, np.timedelta64)):
            return self._add_delta(-other)
        elif is_integer(other):
            return self.shift(-other)
        elif isinstance(other, datetime):
            return self._sub_datelike(other)
        elif isinstance(other, Period):
            return self._sub_period(other)
        else:  # pragma: no cover
            return NotImplemented

    cls.__sub__ = __sub__

    def __rsub__(self, other):
        return -(self - other)

    cls.__rsub__ = __rsub__

    cls.__iadd__ = __add__
    cls.__isub__ = __sub__


# Traceback (OverflowError)
In [9]: pd.to_timedelta(['24658 days 11:15:00', 'NaT']) + pd.Timestamp('1950-01-01')
---------------------------------------------------------------------------
OverflowError                             Traceback (most recent call last)
<ipython-input-9-cc287bf4c401> in <module>()
----> 1 pd.to_timedelta(['24658 days 11:15:00', 'NaT']) + pd.Timestamp('1950-01-01')

~/conda/envs/xarray-py36/lib/python3.6/site-packages/pandas/core/indexes/datetimelike.py in __add__(self, other)
658                 return self.shift(other)
659             elif isinstance(other, (Timestamp, datetime)):
--> 660                 return self._add_datelike(other)
661             else:  # pragma: no cover
662                 return NotImplemented

~/conda/envs/xarray-py36/lib/python3.6/site-packages/pandas/core/indexes/timedeltas.py in _add_datelike(self, other)
354             other = Timestamp(other)
355             i8 = self.asi8
--> 356             result = checked_add_with_arr(i8, other.value)
357             result = self._maybe_mask_results(result, fill_value=iNaT)
358         return DatetimeIndex(result, name=self.name, copy=False)

~/conda/envs/xarray-py36/lib/python3.6/site-packages/pandas/core/algorithms.py in checked_add_with_arr(arr, b, arr_mask, b_mask)
889
890     if to_raise:
--> 891         raise OverflowError("Overflow in int64 addition")
892     return arr + b
893

OverflowError: Overflow in int64 addition

# Fixed code
def _add_datetimelike_methods(cls):
    """
    add in the datetimelike methods (as we may have to override the
    superclass)
    """

    def __add__(self, other):
        from pandas.core.index import Index
        from pandas.core.indexes.timedeltas import TimedeltaIndex
        from pandas.tseries.offsets import DateOffset

        if isinstance(other, TimedeltaIndex):
            return self._add_delta(other)
        elif isinstance(self, TimedeltaIndex) and isinstance(other, Index):
            if hasattr(other, "_add_delta"):
                return other._add_delta(self)
            raise TypeError(
                "cannot add TimedeltaIndex and {typ}".format(typ=type(other))
            )
        elif isinstance(other, (DateOffset, timedelta, np.timedelta64)):
            return self._add_delta(other)
        elif is_integer(other):
            return self.shift(other)
        elif isinstance(other, (Index, datetime, np.datetime64)):
            return self._add_datelike(other)
        else:  # pragma: no cover
            return NotImplemented

    cls.__add__ = __add__
    cls.__radd__ = __add__

    def __sub__(self, other):
        from pandas.core.index import Index
        from pandas.core.indexes.datetimes import DatetimeIndex
        from pandas.core.indexes.timedeltas import TimedeltaIndex
        from pandas.tseries.offsets import DateOffset

        if isinstance(other, TimedeltaIndex):
            return self._add_delta(-other)
        elif isinstance(self, TimedeltaIndex) and isinstance(other, Index):
            if not isinstance(other, TimedeltaIndex):
                raise TypeError(
                    "cannot subtract TimedeltaIndex and {typ}".format(
                        typ=type(other).__name__
                    )
                )
            return self._add_delta(-other)
        elif isinstance(other, DatetimeIndex):
            return self._sub_datelike(other)
        elif isinstance(other, Index):
            raise TypeError(
                "cannot subtract {typ1} and {typ2}".format(
                    typ1=type(self).__name__, typ2=type(other).__name__
                )
            )
        elif isinstance(other, (DateOffset, timedelta, np.timedelta64)):
            return self._add_delta(-other)
        elif is_integer(other):
            return self.shift(-other)
        elif isinstance(other, (datetime, np.datetime64)):
            return self._sub_datelike(other)
        elif isinstance(other, Period):
            return self._sub_period(other)
        else:  # pragma: no cover
            return NotImplemented

    cls.__sub__ = __sub__

    def __rsub__(self, other):
        return -(self - other)

    cls.__rsub__ = __rsub__

    cls.__iadd__ = __add__
    cls.__isub__ = __sub__