如何通过数组删除 JSON object？ （Python）

Question

I know the title looks a little confusing but once I share the code you'll know what I am talking about. I am fairly new to working with JSON and Python overall. I'm trying to make a grocery list program with 3 simple commands: list, add, and remove. List will list all of your groceries that you added via add. Remove removes an item by name. This is where I'm having trouble. This is what my setup looks like:

{"grocery_list": 
   [{"itemname": "Milk"},
   {"itemname": "Bread"},
   {"itemname": "Bacon"}]
}

This is my remove function and data:

with open('groceriesjson.json','r') as data_file:
        data = json.load(data_file)

def removeitem(item):
        global data
        for i in range(len(data)):
            if data[i]["itemname"] == item:
                data.pop(i)
                print("Successfully removed from your list.")
                main()

When I run the program, I get this error:

Traceback (most recent call last):
  File "C:\Users\me\Desktop\test.py", line 48, in <module>
    main()
  File "C:\Users\me\Desktop\test.py", line 44, in main
    removeitem(toremove)
  File "C:\Users\me\Desktop\test.py", line 18, in removeitem
    if data[i]["itemname"] == item:
 KeyError: 0

I have also tried using range(1,len(data)) but when I run it nothing happens. If you need any more snippets of code or anything else please comment. Thanks a lot

Answer 1

You can instead use a list comprehension

values = {
    "grocery_list": [
        {"itemname": "Milk"},
        {"itemname": "Bread"},
        {"itemname": "Bacon"}
    ]
}

print({
    "grocery_list": 
        [v for v in values['grocery_list'] if v['itemname'] != 'Milk']
})

Answer 2

You have failed to test your program in stages; you now have multiple mistakes to correct. See this lovely reference for debugging help . If nothing else, insert frequent print commands to check your assumptions about data types and values.

You do not have a "JSON object"; you have a Python dict . For a better example, remove the input sequence and replace it with the hard-coded dict equivalent. The first step of debugging is to isolate the problem, and this demonstrates that the input is independent.

Now, look at your structure: the dict has one entry, keyed by the string "grocery_list". Your immediate error is that you tried to access this as a list , using subscript 0. This would work well with the next level down, data["grocery_list"], as that is a list.

Next, you will run into problems when you alter a list while you iterate over it. See the related questions on that topic for pointers. The "normal" way is to use a list comprehension, as you see in Sushanth 's answer.

You call a routine main from within your removal loop; this is almost certainly a mistake, especially if that routine is, indeed, your main program. Put in print statements and follow the logic to see how this actually works.

Answer 3

Maybe something like this:

def removeitem(del_item):
        global data
        grocery_list = data['grocery_list']

        for i, item in enumerate(grocery_list):
            if item["itemname"] == del_item:
                grocery_list.pop(i)
                print("Successfully removed from your list.")
                break

        return grocery_list