What are APIs?

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What are APIs?

Webinar

22 March 2016

Peter SmythUK Data Service

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Overview of this webinar

• Description of an API

• Examples of APIs

• Finding and using API documentation

• Browser based Demo of API usage

• Code based demo of using an API

Wikipedia - API Definition

• An API is a set of routines, protocols and tools for building software applications

• It expresses a software component in terms of its operations, inputs, outputs and underlying types

• An API defines functionalities that are independent of their respective implementations

• A programmer can use the API to build an application

An API hides the complexity of implementationUsing an API allows the implementation to change, without affecting users

Generic API

Application A Application B

Response

Request

Who needs to know what?

• Application B needs to be able to correctly format the

requests and to be able to interpret the responses

• Application A needs to be able to understand the

requests and correctly return a response

Who doesn’t need to know what?

• Application A doesn’t need know what application B does

with the response

• Application B doesn’t need to know how Application A

create the responses from the requests

Specific cases

• Application A is some kind of Web serviceo Could be simple website retuning Web pages in

response to a URL requesto Could be providing a data stream in response to a

formatted search request• Application B is a user controlled application

o A Smartphone appo A web browsero A development toolo Program code

Generic API

Application A

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Application B

The flexibility of APIs

The format of the requests and responses is fixed,

but beyond that:

• the requester could be any of many different

sources (previous slide)

• the responder is free to change the manner in

which the response is calculated or found

Who has an API ? - Some examples• Twitter

• https://dev.twitter.com/• Facebook

• https://developers.facebook.com/• Met Office

• http://www.metoffice.gov.uk/datapoint• The Guardian

• http://open-platform.theguardian.com/• Transport API

• http://www.transportapi.com/• Google Maps

• https://developers.google.com/maps/There are many more Google APIs, but the search API is depreciated.

How do you use an API?

[Decide how to formulate the request]

Make a requestGet a response[Work out how to interpret the response]

TransportAPI

• Sample call:

http://transportapi.com/v3/uk/bus/stop/490012745J/live.h

tml?group=route&api_key=d9307fd91b0247c607e098d5

effedc97&app_id=03bf8009

TransportAPI Response{"atcocode": "490012745J","smscode": "47889","request_time": "2015-09-30T10:55:31+01:00","departures": {"243": [{"mode": "bus","line": "243","direction": "Wood Green","operator": "TFL","aimed_departure_time": null,"expected_departure_time": "11:13","best_departure_estimate": "11:13","source": "Countdown instant"

},...

]"55": [{"mode": "bus","line": "55","direction": "Bakers Arms","operator": "TFL","aimed_departure_time": null,"expected_departure_time": "11:08","best_departure_estimate": "11:08","source": "Countdown instant"

},...

],}

}

API Documentation

• Essential to read and understand the API

documentation

o How to format requests

o The format and contents of Responses

o The use of keys

o Limitations on use

Example - The Guardian API

• The documentation• http://open-platform.theguardian.com/access/

• The Guardian Open Platform tool• http://open-platform.theguardian.com/explore/

Fiddler

• Web development tool

• Open Source & Free to download and use

• Capable of many things

o We just want to be able to send requests and

examine the responses

Guardian Example - R code

1. Format a request

2. Send request

3. Get response

4. Parse response to extract the weburls

5. Request the web pages for the URLs

6. For each page create a wordcloud

Twitter Example

• You need to have a Twitter account to use the

API

• You need a set of 4 keys

• Keys are obtained by creating an application

• The starting point is https://apps.twitter.com/

Retrieving Tweets

Either make a search of the available Twitter database (approx. last 7 days of tweets)Oruse the Streaming API to capture Tweets as they occur (only a 1% sample is made available)

In either method, you should have no expectation of completeness

Search Twitter - R code

1. Uses the TwitteR library2. Set up authorisation using the 4 keys3. Search for the keyword ‘brexit’ in separate

searches over a 4 day period4. Save the text of the returned tweets into a data

frame5. Extract the hashtags from the Tweets6. Create a word cloud from the hashtag values

Stream Twitter – Python code

1. Uses the Tweepy package

2. Set up authorisation using the 4 keys

3. Arrange to have the returned Tweets written to

a file

4. Arrange to print the Name, Time and Text from

the Tweet on the screen

What to do when you want to scale up

• Scheduled requesto cron or task scheduler, looping code with

timer delay• More intelligence about the requests to make

(based on previous responses)oMore complex coding

• Persist the returned data for future analysisoWrite responses to a file or a database

API books

Questions

Peter Smyth

Peter.smyth@manchester.ac.uk

ukdataservice.ac.uk/help/

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