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| [[File:Highfivekitten.jpeg|200px|thumb|In which you learn how to use Python and web APIs to meet the likes of her!]]
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| == Lecture Outline ==
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| ;Introduction and context
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| * You can write some tools in Python now. Congratulations!
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| * Today we'll learn how to find/create data sets
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| * Next week we'll get into data science (asking and answering questions)
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| ;Outline:
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| * What is an API?
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| * How do we use one to fetch interesting datasets?
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| * How do we write programs that use the internet?
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| * How can we use the placekitten API to fetch kitten pictures?
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| * Introduction to structured data (JSON)
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| * How do we use APIs in general?
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| ;What is a (web) API?
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| * API: a structured way for programs to talk to each other (aka an interface for programs)
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| * Web APIs: like a website your programs can visit (you:a website::your program:a web API)
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| ; How do we use an API to fetch datasets?
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| Basic idea: your program sends a request, the API sends data back
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| * Where do you direct your request? The site's API endpoint.
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| ** For example: Wikipedia's web API endpoint is http://en.wikipedia.org/w/api.php
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| * How do I write my request? Put together a URL; it will be different for different web APIs.
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| ** Check the documentation, look for code samples
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| * How do you send a request?
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| ** Python has modules you can use, like <code>requests</code> (they make HTTP requests)
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| * What do you get back?
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| ** Structured data (usually in the JSON format)
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| * How do you understand (i.e. parse) the data?
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| ** There's a module for that!
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| ; How do we write Python programs that make web requests?
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| To use APIs to build a dataset we will need:
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| * all our tools from last session: variables, etc
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| * the ability to open urls on the web
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| * the ability to create custom URLS
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| * the ability to save to files
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| * the ability to understand (i.e., parse) JSON data that APIs usually give us
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| ; New programming concepts:
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| * interpolate variables into a string using % and %()s
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| * requests
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| * open files and write to them
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| ; How do we use an API to fetch kitten pictures?
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| [http://placekitten.com/ placekitten.com]
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| * API that takes specially crafted URLs and gives appropriately sized picture of kittens
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| * Exploring placekitten in a browser:
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| ** visit the API documentation
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| ** kittens of different sizes
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| ** kittens in greyscale or color
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| * Now we write a small program to grab an arbitrary square from placekitten by asking for the size on standard in: [http://mako.cc/teaching/2014/cdsw-autumn/placekitten_raw_input.py placekitten_raw_input.py]
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| ; Introduction to structured data (JSON, JavaScriptObjectNotation)
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| * what is json: useful for more structured data
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| * import json; json.loads()
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| * like Python (except no single quotes)
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| * simple lists, dictionaries
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| * can reflect more complicated data structures
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| * Example file at http://mako.cc/cdsw.json
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| * You can parse data directly with <code>.json()</code> on a <code>requests</code> call
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| ; Using other APIs
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| * every API is different, so read the documentation!
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| * If the documentation isn't helpful, search online
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| * for popular APIs, there are python modules that help you make requests and parse json
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| Possible issues:
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| * rate limiting
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| * authentication
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| * text encoding issues
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| == Other Potentially Resources ==
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| My friend Frances gave a version of this lecture last year and create slides. They are written for Python 2, so the code might not all work (remember, use <Code>print()</code> with parentheses) but the basic ideas might be helpful:
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| * [http://mako.cc/teaching/2014/cdsw-autumn/lecture2-web_apis.pdf Slides (PDF)] — For viewing
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| * [http://mako.cc/teaching/2014/cdsw-autumn/lecture2-web_apis.odp Slides (ODP Libreoffice Slides Format)] — For editing and modification
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| [[Category:DS4UX (Spring 2016)]]
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