Connect to a Server

REST follows the client-server model. The server provides endpoints to connect to and serves data as per the request. The client connects to the endpoint and requests data. The request and response always follow the HTTP request-response model. For simplicity, in place of the API endpoint, the term “service” will be used.

The task of connecting to a server can be divided into two types:

• Without configuration
• With configuration

This distinction occurs due to a variety of reasons, including but not limited to, authentication mechanisms used by the server and the certificate type of the server. In this lesson, we’ll look at how to connect to a server without the client needing to configure itself. For completeness, the client will try to fetch data, i.e., issue a GET. We’ll be connecting to the air quality service provided by MET Norway. The URI is as follows:

https://api.met.no/weatherapi/airqualityforecast/0.1/stations.

Previously, we had chosen the requests library to use for our client. Let’s see how to use our chosen library to connect to the service.

Steps

1. Create a new file named client.py.

2. Import the requests library.

import requests

3. Create a class and name it Client.

class Client(object):

4. Add a parameterized constructor that accepts url as a parameter, and assign it to an instance variable.

def __init__(self, url: str):
	self.url = url

5. Create a method named get with the return type as a string.

def get(self) -> str:

6. Within the method, call the get method of requests and pass the URL to it using the instance variable url. Return the body of the response using the content attribute of the response object.

response = requests.get(self.url)
return response.content

7. Add a main block.

if __name__ == '__main__':

8. Create an instance of Client named client by passing the URI of the air quality service.

client = Client(
'https://api.met.no/weatherapi/airqualityforecast/0.1/stations')

9. Call the get method of the client and print the result.

print(client.get())

How it works

The core of the code is in the get method of the Client class. The get method calls the get method of requests. As mentioned earlier, the requests library provides wrappers to make REST calls easier. The get method is one such wrapper. It encapsulates the lower-level details of connecting to the service. The parameter is the URL of the service, which, in this case, is provided by the instance variable url.

The response from the service is represented by the response object, which is returned by the get method. The response object contains, at the minimum, the status code returned by the server and the content if the call has been successful. If the call results in an error, the status code will contain the HTTP error code, and the content might contain the error details. The reason behind saying “might” is that some services just return the error code and no details of the error; other services may provide a link to know more about the error.

As might be guessed, the content attribute of the response object contains the content returned by the service. The get method returns the content as its result, which is then printed by the main block.

Try it yourself

• Follow the steps above to complete the code for this lesson.

• Click “Run” to execute the code and display the result.

Solution

If stuck, refer to the final code below for some guidance.

Please note that the file below is read-only.