How to remove an element from a JSON array using Python?

Question

I'm currently trying to make a Chromebook rental application for my high school that stores checkout information in a JSON file. Everything works except removing data from the JSON array. I found a YouTube video(link) that I thought would work as a solution, so I followed along with that. However, whenever there's more than two elements and I enter anything higher than two, it doesn't delete anything. Even worse, when I enter the number one, it deletes everything but the zero index(whenever the array has more than two elements in it).

Here's the Python code:

def view_data():   # Prints JSON Array to screen
    with open(filename, "r") as f:
        data = json.load(f)
        i = 0
        for item in data:
            name = item["name"]
            chromebook = item["chromebook"]
            check_out = item["time&date"]
            print(f"Index Number: {i}")
            print(f"Name : {name}")
            print(f"Chromebook : {chromebook}")
            print(f"Time Of Checkout: {check_out} ")
            print("\n\n")
            i = i + 1

def delete_data():    # Deletes an element from the array
    view_data()
    new_data = []
    with open(filename, "r") as f:
        data = json.load(f)
        data_length = len(data) - 1
    print("Which index number would you like to delete?")
    delete_option = input(f"Select a number 0-{data_length}: ")
    i = 0
    for entry in data:
        if i == int(delete_option):
            pass
            i = + 1
        else:
            new_data.append(entry)
            i = + 1

    with open(filename, "w") as f:
        json.dump(new_data, f, indent=4)

Here's the JSON file code:

[
{
    "name": "Tyler",
    "chromebook": "12123223",
    "time&date": "Check Out Time: 13:33:22 May-11-2021"
},
{
    "name": "Craig",
    "chromebook": "41222224",
    "time&date": "Check Out Time: 13:33:34 May-11-2021"
},
{
    "name": "Bill",
    "chromebook": "3235223",
    "time&date": "Check Out Time: 13:33:46 May-11-2021"
}
]

For example, say the user wanted to remove the second index in the JSON array. Is there a better way to implement that in my Python script?

I'm still a fairly new and learning Python developer, and if there's any better solution I'm open to suggestions. If you need for info, I'll be active.

Answer 1

import json

data =  json.loads(jsonString) #convert json string to object
delete_option = input(f"Select a number 0-{data_length}: ")
del data[int(delete_option)]

Answer 2

First question

However, whenever there's more than two elements and I enter anything higher than two, it doesn't delete anything. Even worse, when I enter the number one, it deletes everything but the zero index(whenever the array has more than two elements in it).

Inside delete_data() you have two lines reading i = + 1, which just assignes +1 (i.e., 1) to i. Thus, you're never increasing your index. You probably meant to write either i = i+1 or i += 1.

def delete_data():    # Deletes an element from the array
    view_data()
    new_data = []
    with open(filename, "r") as f:
        data = json.load(f)
        data_length = len(data) - 1
    print("Which index number would you like to delete?")
    delete_option = input(f"Select a number 0-{data_length}: ")
    i = 0
    for entry in data:
        if i == int(delete_option):
            i += 1  # <-- here
        else:
            new_data.append(entry)
            i += 1  # <-- and here

    with open(filename, "w") as f:
        json.dump(new_data, f, indent=4)

---

Second question: further improvements

Is there a better way to implement that in my Python script?

First, you can get rid of manually increasing i by using the builtin enumerate generator. Second, you could make your functions reusable by giving them parameters - where does the filename in your code example come from?

# view_data() should probably receive `filename` as a parameter
def view_data(filename: str):   # Prints JSON Array to screen
    with open(filename, "r") as f:
        data = json.load(f)
        # iterate over i and data simultaneously
        # alternatively, you could just remove i
        for i, item in enumerate(data):
            name = item["name"]
            chromebook = item["chromebook"]
            check_out = item["time&date"]
            print(f"Index Number: {i}")
            print(f"Name : {name}")
            print(f"Chromebook : {chromebook}")
            print(f"Time Of Checkout: {check_out} ")
            print("\n\n")
            # not needed anymore: i = i + 1

# view_data() should probably receive `filename` as a parameter
def delete_data(filename: str):    # Deletes an element from the array
    view_data()
    new_data = []
    with open(filename, "r") as f:
        data = json.load(f)
        data_length = len(data) - 1
    print("Which index number would you like to delete?")
    delete_option = input(f"Select a number 0-{data_length}: ")
    # iterate over i and data simultaneously
    for i, entry in enumerate(data):
        if i != int(delete_option):
            new_data.append(entry)

    with open(filename, "w") as f:
        json.dump(new_data, f, indent=4)

Furthermore, you could replace that for-loop by a list comprehension, which some may deem more "pythonic":

new_data = [entry for i, entry in enumerate(data) if i != int(delete_option)]

Answer 3

There are easier ways to delete an element by index from a Python list.

Given li = ["a", "b", "c"], you can delete element 1 ("b") by index in (at least) the following ways:

li.pop(1) # pop takes an index (defaults to last) and removes and returns the element at that index

del li[1] # the del keyword will also remove an element from a list

So, here's some updated code:

def view_data():   # Prints JSON Array to screen
    with open(filename, "r") as f:
        data = json.load(f)
        i = 0
        for item in data:
            name = item["name"]
            chromebook = item["chromebook"]
            check_out = item["time&date"]
            print(f"Index Number: {i}")
            print(f"Name : {name}")
            print(f"Chromebook : {chromebook}")
            print(f"Time Of Checkout: {check_out} ")
            print("\n\n")
            i = i + 1

def delete_data():    # Deletes an element from the array
    view_data()
    with open(filename, "r") as f:
        data = json.load(f)
        data_length = len(data) - 1
    print("Which index number would you like to delete?")
    delete_option = input(f"Select a number 0-{data_length}: ")
    del data[int(delete_option)] # or data.pop(int(delete_option))

    with open(filename, "w") as f:
        json.dump(data, f, indent=4)