How to check if a dictionary element is an array

Python Help
1

I have this line of code that I want to proof check

icon = data[‘weather’][0][‘icon’]

How do I make sure that [0] exists before grabbing ‘icon’ from it?

Thanks.

2

Hi,

welcome to the Python forum. An fyi, please follow these formatting instructions when entering code for better visibility:

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Now, regarding your question, here is an example that hopefully helps you to understand the concept. Note that you do not need to explicitly define the icon string in brackets as per your query. You only need to define its location via diction['d'][1] (dictionary diction, element d, index 1 from the list/array). Note that indexes always start from 0 unless explicitly designed to start from another value.

# Define list array
a_list = [1, 'icon', 3, 4, 5, 6]
# Define dictionary with an array/list as an item value
diction = {'a': 1, 'b': 2, 'c': 3, 'd': a_list}

if diction['d'][1] == 'icon':
    print('Yes, it exists!')
else:
    print('Sorry, it does not exist.')

You can change the spelling of icon to test if it exists.

3

You could do

try:
  weather_first_data = data[‘weather’][0]
except TypeError:
  ... # Complain that `data['weather']` might not be a list
except IndexError:
  ... # Complain that `data['weather']` is empty
icon = weather_data['icon']

If data['data'] is supposed to be a list, perhaps data should belong to a class that ensures the nature of the information that it contains, instead of only a dictionary.

For example, you can write a system of classes using pydantic that defines the OpenWeatherMap API. You feed them the response and they take care of validating the JSON.

1 Like
4

Thank you both. The ‘weather’ data is returned from OpenWeatherMap. Here’s a ‘json.dump’ of the whole variable

{
    "coord": {
        "lon": 0.0,
        "lat": 0.0
    },
    "weather": [
        {
            "id": 800,
            "main": "Clear",
            "description": "clear sky",
            "icon": "01d"
        }
    ],
    "base": "stations",
    "main": {
        "temp": 288.34,
        "feels_like": 287.43,
        "temp_min": 287.14,
        "temp_max": 288.34,
        "pressure": 1019,
        "humidity": 58,
        "sea_level": 1019,
        "grnd_level": 993
    },
    "visibility": 10000,
    "wind": {
        "speed": 1.84,
        "deg": 255,
        "gust": 3.71
    },
    "clouds": {
        "all": 9
    },
    "dt": 1721392609,
    "sys": {
        "type": 2,
        "id": 2003814,
        "country": "CA",
        "sunrise": 1721381569,
        "sunset": 1721436490
    },
    "timezone": -14400,
    "id": 6041177,
    "name": "Lac-Sainte-Marie",
    "cod": 200
}

I want to make sure data[‘weather’][0] exist before fetching ‘icon’ from it.

5

You can do:

if weather := data['weather']:
    icon = weather[0]['icon']

This assumes that data['weather'] exists and is a list, which may be empty.

6

You can use something like this:

try:
    if data['weather'][22]:  # Purposefully entered an `22` for testing purposes (re-enter a '0')
        print('The data point is: ', data['weather'][0]['icon'])

# Catches indexing errors
except IndexError:
    print('The index requested is not valid!')
# Catches if an invalid dictionary was entered or if misspelled.
except KeyError:
    print('The key entered in dictionary, does not exist!')

For this, if you are not already familiar, read up on exception handling to catch any indexing / key errors so that it does not crash your system.

7

You can explicitly check for it:

if len(data['weather']) > 0:
    icon = data[‘weather’][0][‘icon’]
else:
    pass  # Code to run if index 0 doesn't exist because the list is empty.

You may also need checks such as if 'weather' in data: and if 'icon' in data['weather'][0]: as well, depending on the format that OpenWeather returns.

8

You could try Structural Pattern Matching:

match data:
    case {'weather': [{'icon': icon}, *_]}:
        print(icon)