[Tut] Python Create JSON File - Printable Version

[Tut] Python Create JSON File - Printable Version

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[Tut] Python Create JSON File - xSicKxBot - 11-03-2022

Python Create JSON File

5/5 – (1 vote)

Problem Formulation and Solution Overview

This article focuses on working with a JSON file. JSON is an acronym for JavaScript Object Notation. This is a flat-text file formatted based on JavaScript (JS) Syntax.

This file is most commonly noted for its ability to transmit data to/from web applications, such as sending/receiving data from a Server/Client to display or retrieve said data.

The JSON file structure has keys and values similar to a Python Dictionary.

This structure can contain strings, boolean, integers, floats, lists, and much more. This file structure can be as simple or complex as needed.

This article works with Rivers Clothing, a new start-up. They have hired their first three (3) employees. This employee data is displayed as a List of Dictionaries.

Code:
emps = {"hires": [{"ID": 324, "name": "Alex Smith", "title": "Manager"}, {"ID": 325, "name": "Micah Jones", "title": "Designer"}, {"ID": 326, "name": "Sam Quinn", "title": "Coder"}]}

Question: How would we write code to create and work with a JSON File?

Python Create JSON File if Not Exists
Python Create JSON String from List of Dictionaries
Python Create JSON File and Write Data
Python Read JSON File
Python Access JSON Elements
Python Delete JSON Elements

Python Create JSON File if Not Exists

This example creates an empty JSON file if one does not exist in the current working directory.

Code:
import os filename = 'employees.json'
isFile = os.path.isfile(filename) if (not isFile): with open(filename, 'w') as fp: pass
else: print(f'The {filename} file exists.')

The first line in the above code snippet imports Python’s built-in

Code:
os

library. This allows access to and manipulation of files and folders.

The following line declares the JSON file name,

Code:
employees.json

and saves it to the variable

Code:
filename

.

The next line calls the

Code:
os.path.isfile()

function and passes it one (1) argument,

Code:
filename

. This function checks the current directory for the existence of the

Code:
employees.json

file

The first time this code runs, and this file is not found (

Code:
isFile

is False), an empty file is created and placed into the current working directory.

Note: The

Code:
pass

statement is a placeholder code and does nothing when executed. This is used here so a file is created, and nothing else occurs.

If this code is rerun or the file exists, the following message is output to the terminal.

The

Code:
employees.json

file exists.

To create this file in a sub-folder, you would modify the code as follows:

Code:
import os filename = 'files\\employees.json'
isFile = os.path.isfile(filename) if (not isFile): with open(filename, 'w') as fp: pass
else: print(f'The {filename} file exists.')

When this code runs, the files folder is checked for the existence of the

Code:
employees.json

file.

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Python Create JSON String from List of Dictionaries

This example creates a JSON string from a List of Dictionaries.

Code:
import json emps = {"hires" :[{"empID": "RC-3243", "name": "Alexa Smith", "title": "Manager"}, {"empID": "RC-3244", "name": "Micah Jones", "title": "Designer"}, {"empID": "RC-3245", "name": "Sam Quinn", "title": "Coder"}]} json_str = json.dumps(emps, indent=4)
print(json_str)

The above code snippet imports the

Code:
json

library. This library allows access to JSON functions.

The following three (3) lines construct a List of Dictionaries containing data for the new hires. The results save to

Code:
emps

.

Next,

Code:
json.dumps()

is called and passed two (2) arguments: a List of Dictionaries,

Code:
emps

, and for formatting, spaces to indent. The results save to

Code:
json_str

and output to the terminal.

Code:
{"hires": [ { "ID": 3243, "name": "Alexa Smith", "title": "Manager" }, { "ID": 3244, "name": "Micah Jones", "title": "Designer" }, { "ID": 3245, "name": "Sam Quinn", "title": "Coder" }  ]}

Note: The

Code:
json.dumps()

function formats the JSON string. To write this to a file,

Code:
json.dump()

is used.

Python Create JSON File and Write Data

This example writes a List of Dictionaries to a JSON file.

Code:
import os
import json filename = 'employees.json'
isFile = os.path.isfile(filename) emps = {"hires" :[{"ID": 3243, "name": "Alexa Smith", "title": "Manager"}, {"ID": 3244, "name": "Micah Jones", "title": "Designer"}, {"ID": 3245, "name": "Sam Quinn", "title": "Coder"}]} if (not isFile): with open(filename, 'w') as fp: json.dump(emps, fp, indent=4)
else: print(f'An error occurred writing to {filename}.')

The above code snippet adds the two (2) highlighted lines to write the formatted JSON string to the

Code:
employees.json

file.

The contents of this file is as follows:

Code:
{"hires": [ { "ID": 3243, "name": "Alexa Smith", "title": "Manager" }, { "ID": 3244, "name": "Micah Jones", "title": "Designer" }, { "ID": 3245, "name": "Sam Quinn", "title": "Coder" }  ]}

Python Read JSON File

In this example, the JSON file saved earlier is read back in.

Code:
import os
import json filename = 'employees.json'
json_str = '' with open(filename , 'r') as fp: for l in fp: l.replace('\n', '') json_str += l print(json_str)

This code snippet opens, reads the

Code:
employees.json

file and saves it to

Code:
json_str

. Upon each iteration, any additional newline (

Code:
\n

) characters are removed using the

Code:
replace()

function.

Once all lines have been read, the contents of

Code:
json_str

is output to the terminal and is the same as indicated above.

Python Access JSON Elements

This example reads in the previously saved JSON file and accesses the ID element from each hire.

Code:
import os
import json filename = 'employees.json'
json_str = '' with open(filename , 'r') as fp: for l in fp: l.replace('\n', '') json_str += l all_emps = json.loads(json_str)
alexa_id = all_emps['hires'][0]['ID']
sam_id = all_emps['hires'][2]['ID']
print(alexa_id, sam_id)

As outlined earlier in this article, the

Code:
employees.json

file is read in, parsed and saved to

Code:
json_str

.

Then,

Code:
json_str

is loaded using

Code:
json_loads()

and passed one (1) argument, the

Code:
json_str

created above. This gives us access to the elements.

The following lines access the Employee IDs for Alexa and Micah and outputs same to the terminal.

Code:
3243 3245

To iterate and display the

Code:
ID

and

Code:
name

for each new

Code:
hire

, run the following code:

Code:
import os
import json filename = 'employees.json'
json_str = '' with open(filename , 'r') as fp: for l in fp: l.replace('\n', '') json_str += l all_emps = json.loads(json_str) for item in all_emps['hires']: print(item['ID'], item['name'])

Another option is to use List Comprehension to retrieve the data:

Code:
results = [item['ID'] for item in all_emps['hires']]
print(results)

Python Delete Elements

This example reads in the previously saved JSON file and deletes the new hire, Micah Jones.

Code:
import os
import json filename = 'employees.json'
json_str = '' with open(filename , 'r') as fp: for l in fp: l.replace('\n', '') json_str += l all_emps = json.loads(json_str)
idx = 0 for item in all_emps['hires']: if idx == 1: del all_emps['hires'][idx] idx += 1
print(all_emps)

Summary

We hope you enjoyed this article about converting a List of Dictionaries to JSON and everything in between!

Good Luck & Happy Coding!

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