[301] JSON. Tyler Caraza-Harter

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1 [301] JSON Tyler Caraza-Harter

2 Learning Objectives Today JSON differences with Python syntax creating JSON files reading JSON files Read: Sweigart Ch 14 JSON and APIs to the end

3 Python Data Structures and File Formats Python File [ [ name, x, y ], [ alice, 100, 150], [ bob, -10, 80] ]? list of lists

4 Python Data Structures and File Formats Python File [ [ name, x, y ], [ alice, 100, 150], [ bob, -10, 80] ] list of lists name,x,y alice,100,150 bob,-10,80 CSV file We can use CSV files to store data we would want in lists of lists

5 Python Data Structures and File Formats Python File [ [ name, x, y ], [ alice, 100, 150], [ bob, -10, 80] ] list of lists alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts name,x,y alice,100,150 bob,-10,80 CSV file?

6 Python Data Structures and File Formats Python File [ [ name, x, y ], [ alice, 100, 150], [ bob, -10, 80] ] list of lists name,x,y alice,100,150 bob,-10,80 CSV file alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts alice : scores : [10,20,19], bob : scores : [15,23,17,15] JSON file

7 Python Data Structures and File Formats Python File JSON files look almost [ identical to Python code [ name, x, y ], for data structures! [ alice, 100, 150], [ bob, -10, 80] ] list of lists name,x,y alice,100,150 bob,-10,80 CSV file alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts alice : scores : [10,20,19], bob : scores : [15,23,17,15] JSON file

8 Python Data Structures and File Formats Python File JSON files look almost [ identical to Python code [ name, x, y ], for data structures! [ alice, 100, 150], [ bob, -10, 80] ] list of lists name,x,y alice,100,150 bob,-10,80 CSV file alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts dicts use curly braces alice : scores : [10,20,19], bob : scores : [15,23,17,15] JSON file

9 Python Data Structures and File Formats Python File JSON files look almost [ identical to Python code [ name, x, y ], for data structures! [ alice, 100, 150], [ bob, -10, 80] ] list of lists keys are separated from values with a colon alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts name,x,y alice,100,150 bob,-10,80 CSV file alice : scores : [10,20,19], bob : scores : [15,23,17,15] JSON file

10 Python Data Structures and File Formats Python File JSON files look almost [ identical to Python code [ name, x, y ], for data structures! [ alice, 100, 150], [ bob, -10, 80] ] list of lists name,x,y alice,100,150 bob,-10,80 CSV file alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts lists use square brackets alice : scores : [10,20,19], bob : scores : [15,23,17,15] JSON file

11 Python Data Structures and File Formats Python File JSON files look almost [ identical to Python code [ name, x, y ], for data structures! [ alice, 100, 150], [ bob, -10, 80] ] list of lists name,x,y alice,100,150 bob,-10,80 CSV file alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts strings are in quotes alice : scores : [10,20,19], bob : scores : [15,23,17,15] JSON file

12 Python Data Structures and File Formats Python File JSON files look almost [ identical to Python code [ name, x, y ], for data structures! [ alice, 100, 150], [ bob, -10, 80] ] list of lists name,x,y alice,100,150 bob,-10,80 CSV file alice : scores : [10,20,19], bob : scores : [15,23,17,15] dict of dicts integers look like integers alice : scores : [10,20,19], bob : scores : [15,23,17,15] JSON file

13 JSON Stands for JavaScript Object Notation JavaScript is a language for web development JSON was developed as a way for JavaScript programs to store/ share data JavaScript is similar to Python, which is why JSON looks like Python code

14 JSON Stands for JavaScript Object Notation JavaScript is a language for web development JSON was developed as a way for JavaScript programs to store/ share data JavaScript is similar to Python, which is why JSON looks like Python code Minor JavaScript vs. Python differences entail gotchas: Python JSON Booleans True, False true, false No value None null Quotes Single ( ) or double ( ) Only double ( ) Commas Extra allowed: [1,2,] No extra: [1,2] Keys Any type: 1: one Str only: 1 : one

15 Reading JSON Files JSON file saved somewhere alice : 10, bob : 12, cindy : 15

16 Reading JSON Files Python Program Parsing Code JSON file saved somewhere alice : 10, bob : 12, cindy : 15

17 Reading JSON Files Python Program dict alice :10, bob :12, cindy :15 Parsing Code JSON file saved somewhere alice : 10, bob : 12, cindy : 15

18 Reading JSON Files Python Program Analysis Code data[ cindy ] 15 dict alice :10, bob :12, cindy :15 Parsing Code JSON file saved somewhere alice : 10, bob : 12, cindy : 15

19 Reading JSON Files Python Program Analysis Code data[ cindy ] 15 dict alice :10, bob :12, cindy :15 Parsing Code JSON file saved somewhere alice : 10, bob : 12, cindy : 15 What does this look like?

20 Reading JSON Files import json def read_json(path): with open(path) as f: return json.load(f) dict Python Program Analysis Code data[ cindy ] 15 alice :10, bob :12, cindy :15 Parsing Code JSON file saved somewhere alice : 10, bob : 12, cindy : 15 What does this look like?

21 Reading JSON Files import json def read_json(path): with open(path) as f: return json.load(f) dict Python Program Analysis Code data[ cindy ] 15 alice :10, bob :12, cindy :15 what about writing? Parsing Code JSON file saved somewhere alice : 10, bob : 12, cindy : 15 What does this look like?

22 Writing JSON Files Python Program Code dict

23 Writing JSON Files Python Program Code data[ cindy ] = 15 dict cindy : 15

24 Writing JSON Files Python Program Code data[ cindy ] = 15 dict cindy : 15 Serialization Code

25 Writing JSON Files Python Program Code data[ cindy ] = 15 dict cindy : 15 Serialization Code JSON file saved somewhere cindy : 15

26 Writing JSON Files Python Program Code data[ cindy ] = 15 dict cindy : 15 Serialization Code What does this look like? JSON file saved somewhere cindy : 15

27 Writing JSON Files Python Program Code data[ cindy ] = 15 dict cindy : 15 Serialization Code What does this look like? JSON file saved somewhere cindy : 15

28 Writing JSON Files Python Program Code data[ cindy ] = 15 import json dict def write_json(path, data): with open(path, 'w') as f: return json.dump(data, f, indent=2) cindy : 15 Serialization Code What does this look like? JSON file saved somewhere cindy : 15

29 Demo: Scores over Time Goal: record scores (save across runs) and print average Input: A name and a score to record Output: Running average for that person Example: prompt> python record.py alice 10 Alice Avg: 10 prompt> python record.py alice 20 Alice Avg: 15 prompt> python record.py bob 13 Bob Avg: 13

So, if you receive data from a server, in JSON format, you can use it like any other JavaScript object.

So, if you receive data from a server, in JSON format, you can use it like any other JavaScript object. What is JSON? JSON stands for JavaScript Object Notation JSON is a lightweight data-interchange format JSON is "self-describing" and easy to understand JSON is language independent * JSON uses JavaScript