def get_distance(self, zip1, zip2):
        '''Returns the distance between two points on the earth.
        
        Inputs used are:
            Longitude (in radians) of the first location,
            Latitude (in radians) of the first location,
            Longitude (in radians) of the second location, and
            Latitude (in radians) of the second location.
        To convert to radians (from degrees), use pythons math.radian function (Note: already done 
        for you in the constructor above).  Returns the distance in miles.'''

        long_1 = self.zips[zip1].longitude
        lat_1  = self.zips[zip1].latitude

        long_2 = self.zips[zip2].longitude
        lat_2  = self.zips[zip2].latitude

        dlong = long_2 - long_1
        dlat = lat_2 - lat_1
        a = (math.sin(dlat / 2))**2 + math.cos(lat_1) * math.cos(lat_2) * (math.sin(dlong / 2))**2
        c = 2 * math.asin(min(1, math.sqrt(a)))
        dist = 3956 * c
        return dist
Returns the distance between two points on the earth.
        
        Inputs used are:
            Longitude (in radians) of the first location,
            Latitude (in radians) of the first location,
            Longitude (in radians) of the second location, and
            Latitude (in radians) of the second location.
        To convert to radians (from degrees), use pythons math.radian function (Note: already done 
        for you in the constructor above).  Returns the distance in miles.
recipes/Python/393241_Calculating_distance_between_zip/recipe-393241.py