1

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.

Improve this question
1
  • del data[delete_option] Commented May 11, 2021 at 19:25

3 Answers 3

Reset to default
3

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)]
Improve this answer
Sign up to request clarification or add additional context in comments.

3 Comments

I appreciate the improvement recommendations, and to answer your question the filename is currently hard coded in as a global variable. Although it's hard coded only for testing, I like your solutions. Thanks much!
As I'm reviewing the code, I noticed you pass the parameter "(filename: str):". I understand why you would pass an argument, but what does the ": str" do? Does that check to make sure the argument is a string?
@Vincent that's just a "type hint" as defined in PEP-484. Type hints are just a hint to your IDE (or type checkers) which type you'd expect there, but do not perform any type checks at runtime. You could just write the argument without a type hint and get the same result. With type hints, your IDE can provide better autocompletion and type checkers (e.g., mypy) can statically analyze if your code adheres to these hints.
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)
Improve this answer

Comments

-3 
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)]
Improve this answer

7 Comments

Please update your answer with the full error traceback.
@quamrana it is an answer so no need for traceback. But some explanation with the answer is always better.
@Opsse I think that if the poster was claiming an error, we would need to see the full error traceback.
@quamrana maybe I missed something but the question doesn't mention an error. And we expect that the answer to don't have it neither, so I don't understand what you want here.
Answer's are great. But for best practices, please provide an explanation. You only posting code makes the OP and future commers copy and paste your answer without understanding the logic behind the answer. Please provide an answer with some explanation. Thank You!
|

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.