def get_known_urls(file_root, cities):
    urls = {}
    for key in cities:
        city = key.replace(' ', '_')
        file_path = f'{file_root}/{city}/urls.txt'
        city_urls = set()
        if os.path.exists(file_path):
            with open(file_path, 'r') as f:
                lines = f.readlines()
                for line in lines:
                    city_urls.add(line.strip())
        urls[key] = city_urls
    return urls
def get_known_urls(file_root, cities):
    urls = {}
    for key in cities:
        city = key.replace(' ', '_')
        file_path = f'{file_root}/{city}/urls.txt'
        city_urls = set()
        if os.path.exists(file_path):
            with open(file_path, 'r') as f:
                lines = f.readlines()
                for line in lines:
                    city_urls.add(line.strip())
        urls[key] = city_urls
    return urls