appending data to a list in a json file

Question

i am making something to monitor a site for new products, so im trying to add all the titles to a json file, that starts out with {"product_titles": []}, im trying to figure our how to add the dicts that contain the product title and sizes to the empty list this is my code

import requests
import json

url = 'https://www.supremenewyork.com/mobile_stock.json'
headers = {
    'User-Agent': 'Mozilla/5.0 (iPhone; CPU iPhone OS 12_1_4 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0 Mobile/15E148 Safari/604.1',
    'Accept': 'application/json',
    'Accept-Encoding': 'br, gzip, deflate',
    'Accept-Language': 'en-us'
}


req = requests.get(url, headers=headers)#

page = req.json()
categories = page['products_and_categories']
Sweatshirts = categories['Sweatshirts']


product_list = []
for sweater in Sweatshirts:
    product_name = sweater['name']
    product_colors = []
    product_sizes = []
    product_stock_levels = []
    #print(product_name)
    raw_product_info = requests.get('https://www.supremenewyork.com/shop/' + str(sweater['id']) + '.json', headers=headers)
    product_info = raw_product_info.json()
    styles = product_info['styles']
    for style in styles:
        colors = style['name']
        full_product_name = product_name + colors
        file = open
        product_colors.append(colors)
        for size in style['sizes']:
            sizes = {size['name'] : size['stock_level']}
            product_sizes.append(sizes)
            with open('supreme.json', 'r+') as supremef:
                data = json.load(supremef)
                dump = json.dump(data['product_titles'].append({full_product_name: sizes}), supremef)

the last few lines in where i try to add it to the list in the json file but its not adding it to it

Please check if you showed us the whole code, at least the import of the `requests` module seems to be missing. — Maurice, Mar 10 '19 at 15:41
Can you verify that `data` get's updated correctly before you dump it with `data['product_titles'].append({full_product_name: sizes})` ? i.e. check, that the list of `'product_titles'` gets extended as expected? Without seeing the supreme.json this is difficult to debug ;-) — Maurice, Mar 10 '19 at 15:52
yea thats the problem im getting, im trying to figure out how to add it to list in the json file — Kendall Kelly, Mar 10 '19 at 15:59

score 1 · Answer 1 · answered Mar 10 '19 at 17:08

As pointed out by @t.m.adam in the comments - here's a little explanation.

You expect the append-operation to return the whole object, which json.dump is then supposed to save.

This example shows this doesn't work, as append returns None.

>>> mydict = {"items": [1,2,3,4]}
>>> type(mydict["items"].append(5))
<class 'NoneType'>
>>> print(mydict)
{'items': [1, 2, 3, 4, 5]}
>>>

See also this question for a discussion on this behaviour, I couldn't find an entry in the Python docs for this.

Your code should probably look like this:

data = json.load(supremef)
data['product_titles'].append({full_product_name: sizes})
dump = json.dump(data, supremef)

Slightly off topic:

Your file = open probably doesn't do what you expect.

appending data to a list in a json file

1 Answers1