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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 _get_day_of_month(other, day_option):
 """Find the day in `other`'s month that satisfies a BaseCFTimeOffset's onOffset policy, as described by the `day_option` argument. Parameters other : cftime.datetime day_option : 'start', 'end' 'start': returns 1 'end': returns last day of the month Returns ------- day_of_month : int """


    if day_option == 'start':
        return 1
    elif day_option == 'end':
        days_in_month = _days_in_month(other)
        return days_in_month
    elif day_option is None:
        # Note: unlike `_shift_month`, _get_day_of_month does not
        # allow day_option = None
        raise NotImplementedError
    else:
        raise ValueError(day_option)