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Lec 21 Web APIs

Assignment Updates​

Stuff due soon:

  • HW7 Due 5/15
  • Capstone Project Presentations 5/16 and 5/17
  • Quiz due Thursday

Slides​

Notes​

APIs​

  • What is an API?
    • Application Programming Interface: A set of functions exposed by a service that allows you to interact with the service
    • Allows you to interact with a service without having to know how the service works
    • Example: Google Maps API
      • Allows you to get directions, find places, etc.
      • You don't need to know how Google Maps works to use it
      • You just need to know how to use the API
  • What is a Web API
  • How do you use an API?
    • You make a request to the API
    • The API returns a response
    • The response contains the data you requested
  • Web APIs
    • APIs that are exposed over the internet
    • You make a request to a URL
    • The response is returned in a format like JSON (python dictionary) usually
    • Example: Google Maps API
      • You make a request to a URL
      • The response is returned in JSON format
      • You can then parse the JSON and use the data
  • Example: https://catfact.ninja/#/Facts/getRandomFact
    • This is an API that returns a random cat fact
    • Click the "Try it out" button to get a random cat fact!

JSON​

  • The cat fact API returns a response in JSON format
  • What is JSON
    • JSON = JavaScript Object Notation
    • It's basically a python dictionary

URLlib​

  • How do we make a request to an API?
  • One way: urllib
    • urllib is a builtin python library that allows you to make requests to URLs
  • Example:
import urllib.request
url = "https://catfact.ninja/fact"
response = urllib.request.urlopen(url)
print(response.read())
  • This returns a response in bytes (notice the b at the front):
b'{"fact":"Cats have individual preferences for scratching surfaces and angles. Some are horizontal scratchers while others exercise their claws vertically.","length":145}'
  • We can decode it to a string, and then parse it as JSON using the json library:
import urllib.request
import json
url = "https://catfact.ninja/fact"
response = urllib.request.urlopen(url)
response_string = response.read().decode('utf-8')
response_dict = json.loads(response_string)
print(response_dict)
  • This prints:
{'fact': 'Cats have individual preferences for scratching surfaces and angles. Some are horizontal scratchers while others exercise their claws vertically.', 'length': 145}

Requests​

  • Urlib is a little bit clunky
  • There is a better library called requests
    • requests is a third party library that you need to install
    • You can install it with pip install requests (or pip3 install requests)
  • New Code:
import requests
url = "https://catfact.ninja/fact"
response = requests.get(url)
response_dict = response.json()
print(response_dict)
  • This prints:
{'fact': 'Cats have individual preferences for scratching surfaces and angles. Some are horizontal scratchers while others exercise their claws vertically.', 'length': 145}
  • Didn't have to decode the response to a string
  • Didn't have to parse the string as JSON
  • requests does all of this for us

Activity​

API Keys​

Not covered in class, but here if anyone is curious

  • Some APIs require an API key
    • An API key is a unique identifier that is used to authenticate you when you make a request to an API
    • It is used to track your usage of the API, and to prevent abuse. Also, it allows the API to charge you if it is a paid API
  • If an API requires an API key, you will need to register for one
    • You will need to go to the API's website and register for an API key
    • You will then need to pass the API key in the request
  • Example: https://openweathermap.org/api
  • We won't cover this in class, but ask chatGPT if you want to know more