Get Latitude and Longitude from Google Maps Geocoding API with Python urllib Library

On Google map, we can find a location with both latitude and longitude, or reversely, from an address, we can find out its latitude and longitude. 

From Google Maps Geocoding API documentation, we need to get an API key first. This key should be kept secret. It is required when we do the requests from the API. 

Also from the documentation, we can get a base url for any queries, this url is ended with a '?', we need to construct the second half of the query url to form a complete working url as the server's host address. Python's urllib.parse module has a great way to convert a dictionary into an encoded url - 'urlencode()' method, we only need to provide two keys to this dictionary parameter - 'address' and 'key' - and their corresponding values. 

Once the url is correctly formatted, we can use urllib.request module to send requests to the url and receive reponses, the method is urlopen(). 

To correctly format the response, we should read() it like we read a file, then decode() it into string. For easier access to the keys inside the data such as 'lat' (for latitude) and 'lng' (for longitude), we use json.loads() to convert them to a dictionary. 

To get necessary data from the dictionary, we only need to track down to the right keys in the dictionary.

Now, let's see how to code this.

'''Use Google Maps GeoCoding API to get a place's 
    latitude and longitude as well as formatted address.
    With both latitude and longitude, we can put a marker on the
    map  for that address'''
    
import urllib.parse, urllib.request
import json

# retrieve the api key from a secret file
with open('google_map.txt', 'r')  as file:
    key = file.read().split()[2].strip()

def get_lat_lng(address):

    # get base_url from google map api doc
    base_url = f'https://maps.googleapis.com/maps/api/geocode/json?'
    
    # use urllib library for converting dic into query string
    query_url = urllib.parse.urlencode({'address': address, 'key': key})
    
    # To form the complete url
    url = base_url + query_url

    # send request to the url and get response
    with urllib.request.urlopen(url) as response:
    
        # read response (HTTPResponse) into bytes, then string, then dict (json)        
        data = json.loads(response.read().decode())
        
        # in case address provided is not real
        if data['status'] != 'OK' or 'status' not in data:
            data = None

    # To read the json file
    # print(json.dumps(data, indent=4))

    # To check the request status
    # print(data['status'])

    # to get lat and lng
    if data != None:
        location= data['results'][0]['geometry']['location']
        lat = location['lat']
        lng = location['lng']
        formatted_address = data['results'][0]['formatted_address']
        return lat, lng, formatted_address
    else:
        print('try again')
        return 

print(get_lat_lng("sumiao juancheng"))

To run this program, we can choose to type in any city or address, I am using a small town in China, it correctly prints out the latitude, longitude and the formatted address with postal code. Very impressive for the accuracy.

To get the source code, go to github