calucalting a feature from 2 dataframes

Question

I am looking to calculate a feature named distance By latitude and longitude from 2 dataframes

| longitude | latitude | distance|
|:----      |:------ : | -----  :|
| 6.484708  | 43.506405|        ?|
| 5.487838  | 43.559794|        ?|
| 3.487838  | 43.218794|        ?|


| longitude | latitude | 
|:----      |:------  :| 
| 6.284471  | 43.506405| 
| 5.187238  | 43.545311| 
| 7.487858  | 43.561234| 

I am using the haversine_distance function to calculate the distance

def haversine_distance(lat1, lon1, lat2, lon2):
   r = 6371
   phi1 = np.radians(lat1)
   phi2 = np.radians(lat2)
   delta_phi = np.radians(lat2 - lat1)
   delta_lambda = np.radians(lon2 - lon1)
   a = np.sin(delta_phi / 2)**2 + np.cos(phi1) * np.cos(phi2) *   np.sin(delta_lambda / 2)**2
   res = r * (2 * np.arctan2(np.sqrt(a), np.sqrt(1 - a)))
   return np.round(res, 2)

but i am having a trouble when i am iterating over 2 dataframes

distances_km = []
for row in df1.itertuples(index=False):
   distances_km.append(
       haversine_distance(row.latitude, row.longitude, df2.latitude, df2.longitude)
   )


df1['distance'] = distances_km