Extracting Specific Keys from JSON Lists and Downloading Images with Python

In the e‑commerce startup context, creating product assets can be costly, so the article shows how to programmatically fetch image URLs from a website and store them locally.

The first utility function extract_key_from_json_list(json_list, key) iterates over a list of JSON objects, extracts the value associated with the specified key, and returns a new list.

def extract_key_from_json_list(json_list, key):
    extracted_list = []
    for json_obj in json_list:
        if key in json_obj:
            extracted_list.append(json_obj[key])
    return extracted_list

This function accepts a list of dictionaries ( json_list ) and a target key, checks each dictionary for the key, and collects the corresponding values.

An example usage demonstrates extracting the "name" field from a sample list of dictionaries:

json_list = [
    {"name": "Alice", "age": 25, "city": "New York"},
    {"name": "Bob", "age": 30, "city": "San Francisco"},
    {"name": "Charlie", "age": 35}
]
extracted_list = extract_key_from_json_list(json_list, "name")
print(extracted_list)
# Output: ['Alice', 'Bob', 'Charlie']

The second utility, download_images(image_list, output_folder) , uses the requests library to download each image URL and saves the files with numeric filenames in the specified folder.

import os
import requests

def download_images(image_list, output_folder):
    if not os.path.exists(output_folder):
        os.makedirs(output_folder)
    for index, image_url in enumerate(image_list):
        try:
            response = requests.get(image_url)
            response.raise_for_status()
            file_name = str(index) + '.jpg'  # numeric index as filename
            file_path = os.path.join(output_folder, file_name)
            with open(file_path, 'wb') as file:
                file.write(response.content)
            print(f"Downloaded {file_name}")
        except requests.exceptions.RequestException as e:
            print(f"Error downloading image at index {index}: {str(e)}")

# Example usage
image_urls = [
    'https://example.com/image1.jpg',
    'https://example.com/image2.jpg',
    'https://example.com/image3.jpg'
]
output_folder = 'images'
download_images(image_urls, output_folder)

The function creates the output directory if it does not exist, iterates over the URLs, downloads each image, and saves it with a sequential numeric name, printing a status message for each successful download.

Finally, an extended version of extract_key_from_json_list shows how to skip JSON objects where the type field equals 3 while still extracting the desired key.

def extract_key_from_json_list(json_list, key):
    extracted_list = []
    for json_obj in json_list:
        if json_obj.get('type') != 3 and key in json_obj:
            extracted_list.append(json_obj[key])
    return extracted_list

json_list = [
    {"type": 1, "name": "Alice", "age": 25},
    {"type": 2, "name": "Bob", "age": 30},
    {"type": 3, "name": "Charlie", "age": 35},
    {"type": 1, "name": "Dave", "age": 40}
]
extracted_list = extract_key_from_json_list(json_list, "name")
print(extracted_list)
# Output: ['Alice', 'Bob', 'Dave']

This variant filters out entries with type == 3 before collecting the specified key values, demonstrating a simple way to apply conditional logic during extraction.