from itertools import chain


message_content = ""
images = []
data = [
    [
        {
            "height": 756,
            "image_key": "img_v3_0277_2c2fbab4-8b13-4a6a-a273-e0d1d47b4ecg",
            "tag": "img",
            "width": 529,
        }
    ],
    [
        {"style": [], "tag": "text", "text": "11111111"},
        {"style": [], "tag": "at", "user_id": "@_user_1", "user_name": "官方应用指令"},
        {"style": [], "tag": "text", "text": ""},
    ],
]


for item in chain.from_iterable(data):
    if item.get("tag") == "text":
        message_content += item["text"]

    if item.get("tag") == "img":
        images.append(item["image_key"])


print(message_content)
print(images)