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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def find_in_sorted_index(dts, dt):
 """ Find the index of ``dt`` in ``dts``. This function should be used instead of `dts.get_loc(dt)` if the index is large enough that we don't want to initialize a hash table in ``dts``. In particular, this should always be used on minutely trading calendars. Parameters dts : pd.DatetimeIndex Index in which to look up ``dt``. **Must be sorted**. dt : pd.Timestamp ``dt`` to be looked up. Returns ------- ix : int Integer index such that dts[ix] == dt. Raises ------ KeyError If dt is not in ``dts``. """

    ix = dts.searchsorted(dt)
    if ix == len(dts) or dts[ix] != dt:
        raise LookupError("{dt} is not in {dts}".format(dt=dt, dts=dts))
    return ix