How can I increase DataFrame's apply function efficiency?

I know it is kinds of impossible but I still look forward to an alternative. Here is my DataFrame (read from csv file):

I need to recognize the country and continent where the location is, and here is my idea:

import pandas as pd
! pip install geopy pycountry_convert

from geopy.geocoders import Nominatim
import pycountry_convert as pc

def geo(text):
  if text:
    try:
      country = geolocator.geocode(text, language='en')[0].split(', ')[-1]
      country_code = pc.country_name_to_country_alpha2(country, cn_name_format="default")
      continent_code = pc.country_alpha2_to_continent_code(country_code)
      return country_code, country, continent_code, continents[continent_code]
    except:
      return None, None, None, None
  else:
    return None, None, None, None
continents = {
    'NA': 'North America',
    'SA': 'South America', 
    'AS': 'Asia',
    'OC': 'Oceania',
    'AF': 'Africa',
    'EU': 'Europe'
}

geolocator = Nominatim()
country_dict = json.loads("{\"AD\":\"Europe\",\"AE\":\"Asia\",\"AF\":\"Asia\",\"AG\":\"North America\",\"AI\":\"North America\",\"AL\":\"Europe\",\"AM\":\"Asia\",\"AN\":\"North America\",\"AO\":\"Africa\",\"AQ\":\"Antarctica\",\"AR\":\"South America\",\"AS\":\"Australia\",\"AT\":\"Europe\",\"AU\":\"Australia\",\"AW\":\"North America\",\"AZ\":\"Asia\",\"BA\":\"Europe\",\"BB\":\"North America\",\"BD\":\"Asia\",\"BE\":\"Europe\",\"BF\":\"Africa\",\"BG\":\"Europe\",\"BH\":\"Asia\",\"BI\":\"Africa\",\"BJ\":\"Africa\",\"BM\":\"North America\",\"BN\":\"Asia\",\"BO\":\"South America\",\"BR\":\"South America\",\"BS\":\"North America\",\"BT\":\"Asia\",\"BW\":\"Africa\",\"BY\":\"Europe\",\"BZ\":\"North America\",\"CA\":\"North America\",\"CC\":\"Asia\",\"CD\":\"Africa\",\"CF\":\"Africa\",\"CG\":\"Africa\",\"CH\":\"Europe\",\"CI\":\"Africa\",\"CK\":\"Australia\",\"CL\":\"South America\",\"CM\":\"Africa\",\"CN\":\"Asia\",\"CO\":\"South America\",\"CR\":\"North America\",\"CU\":\"North America\",\"CV\":\"Africa\",\"CX\":\"Asia\",\"CY\":\"Asia\",\"CZ\":\"Europe\",\"DE\":\"Europe\",\"DJ\":\"Africa\",\"DK\":\"Europe\",\"DM\":\"North America\",\"DO\":\"North America\",\"DZ\":\"Africa\",\"EC\":\"South America\",\"EE\":\"Europe\",\"EG\":\"Africa\",\"EH\":\"Africa\",\"ER\":\"Africa\",\"ES\":\"Europe\",\"ET\":\"Africa\",\"FI\":\"Europe\",\"FJ\":\"Australia\",\"FK\":\"South America\",\"FM\":\"Australia\",\"FO\":\"Europe\",\"FR\":\"Europe\",\"GA\":\"Africa\",\"GB\":\"Europe\",\"GD\":\"North America\",\"GE\":\"Asia\",\"GF\":\"South America\",\"GG\":\"Europe\",\"GH\":\"Africa\",\"GI\":\"Europe\",\"GL\":\"North America\",\"GM\":\"Africa\",\"GN\":\"Africa\",\"GP\":\"North America\",\"GQ\":\"Africa\",\"GR\":\"Europe\",\"GS\":\"Antarctica\",\"GT\":\"North America\",\"GU\":\"Australia\",\"GW\":\"Africa\",\"GY\":\"South America\",\"HK\":\"Asia\",\"HN\":\"North America\",\"HR\":\"Europe\",\"HT\":\"North America\",\"HU\":\"Europe\",\"ID\":\"Asia\",\"IE\":\"Europe\",\"IL\":\"Asia\",\"IM\":\"Europe\",\"IN\":\"Asia\",\"IO\":\"Asia\",\"IQ\":\"Asia\",\"IR\":\"Asia\",\"IS\":\"Europe\",\"IT\":\"Europe\",\"JE\":\"Europe\",\"JM\":\"North America\",\"JO\":\"Asia\",\"JP\":\"Asia\",\"KE\":\"Africa\",\"KG\":\"Asia\",\"KH\":\"Asia\",\"KI\":\"Australia\",\"KM\":\"Africa\",\"KN\":\"North America\",\"KP\":\"Asia\",\"KR\":\"Asia\",\"KW\":\"Asia\",\"KY\":\"North America\",\"KZ\":\"Asia\",\"LA\":\"Asia\",\"LB\":\"Asia\",\"LC\":\"North America\",\"LI\":\"Europe\",\"LK\":\"Asia\",\"LR\":\"Africa\",\"LS\":\"Africa\",\"LT\":\"Europe\",\"LU\":\"Europe\",\"LV\":\"Europe\",\"LY\":\"Africa\",\"MA\":\"Africa\",\"MC\":\"Europe\",\"MD\":\"Europe\",\"ME\":\"Europe\",\"MG\":\"Africa\",\"MH\":\"Australia\",\"MK\":\"Europe\",\"ML\":\"Africa\",\"MM\":\"Asia\",\"MN\":\"Asia\",\"MO\":\"Asia\",\"MP\":\"Australia\",\"MQ\":\"North America\",\"MR\":\"Africa\",\"MS\":\"North America\",\"MT\":\"Europe\",\"MU\":\"Africa\",\"MV\":\"Asia\",\"MW\":\"Africa\",\"MX\":\"North America\",\"MY\":\"Asia\",\"MZ\":\"Africa\",\"NA\":\"Africa\",\"NC\":\"Australia\",\"NE\":\"Africa\",\"NF\":\"Australia\",\"NG\":\"Africa\",\"NI\":\"North America\",\"NL\":\"Europe\",\"NO\":\"Europe\",\"NP\":\"Asia\",\"NR\":\"Australia\",\"NU\":\"Australia\",\"NZ\":\"Australia\",\"OM\":\"Asia\",\"PA\":\"North America\",\"PE\":\"South America\",\"PF\":\"Australia\",\"PG\":\"Australia\",\"PH\":\"Asia\",\"PK\":\"Asia\",\"PL\":\"Europe\",\"PM\":\"North America\",\"PN\":\"Australia\",\"PR\":\"North America\",\"PS\":\"Asia\",\"PT\":\"Europe\",\"PW\":\"Australia\",\"PY\":\"South America\",\"QA\":\"Asia\",\"RE\":\"Africa\",\"RO\":\"Europe\",\"RS\":\"Europe\",\"RU\":\"Europe\",\"RW\":\"Africa\",\"SA\":\"Asia\",\"SB\":\"Australia\",\"SC\":\"Africa\",\"SD\":\"Africa\",\"SE\":\"Europe\",\"SG\":\"Asia\",\"SH\":\"Africa\",\"SI\":\"Europe\",\"SJ\":\"Europe\",\"SK\":\"Europe\",\"SL\":\"Africa\",\"SM\":\"Europe\",\"SN\":\"Africa\",\"SO\":\"Africa\",\"SR\":\"South America\",\"ST\":\"Africa\",\"SV\":\"North America\",\"SY\":\"Asia\",\"SZ\":\"Africa\",\"TC\":\"North America\",\"TD\":\"Africa\",\"TF\":\"Antarctica\",\"TG\":\"Africa\",\"TH\":\"Asia\",\"TJ\":\"Asia\",\"TK\":\"Australia\",\"TM\":\"Asia\",\"TN\":\"Africa\",\"TO\":\"Australia\",\"TR\":\"Asia\",\"TT\":\"North America\",\"TV\":\"Australia\",\"TW\":\"Asia\",\"TZ\":\"Africa\",\"UA\":\"Europe\",\"UG\":\"Africa\",\"US\":\"North America\",\"UY\":\"South America\",\"UZ\":\"Asia\",\"VC\":\"North America\",\"VE\":\"South America\",\"VG\":\"North America\",\"VI\":\"North America\",\"VN\":\"Asia\",\"VU\":\"Australia\",\"WF\":\"Australia\",\"WS\":\"Australia\",\"YE\":\"Asia\",\"YT\":\"Africa\",\"ZA\":\"Africa\",\"ZM\":\"Africa\",\"ZW\":\"Africa\"}")
test['GEO'] = test['LOCATION'].apply(geo)

It looks like this would run forever because my dataframe has more than 500 million records. Can I still improve it?

First some soapboxing about slow code: you really should profile your code to understand why/where it's slow before trying to make it faster. In your case,geolocator.geocode makes a network call (probably rate limited) which takes ~1 second; for a 500m row dataframe, that will take ~15 years to complete. Dask/swifter/spark are not the right solution to this problem either, and will waste compute needlessly without making it much faster (maybe only 3 years :).

To solve the problem at hand: geolocator.geocode just tries to get the country name - but it's easy to get all values locally to try. A minimal adaptation that will improve performance by orders of magnitude would look like this:

# find a package that contains country names
!pip install country_list
from country_list import available_languages
country_dict = dict(countries_for_language('en'))
COUNTRIES = set(country_dict.values())


def geo(text):
  if text:
    try:
      country_name = text.split(", ")[-1]
      if country_name in COUNTRIES:
        country_code = pc.country_name_to_country_alpha2(country_name, cn_name_format="default")
      continent_code = pc.country_alpha2_to_continent_code(country_code)
      return country_code, country_name, continent_code, continents[continent_code]
    except:
      return None, None, None, None
  else:
    return None, None, None, None

This should run a million times faster (maybe literally). You could improve on this with better parsing of your location values, but this will be a huge lift.