Upload YouTube Shorts in Python:
YouTube Data API v3, Simplified

from multi_upload_tool import MultiUploadClient

client = MultiUploadClient(api_token="YOUR_API_TOKEN")

# Upload Short with custom thumbnail + playlist assignment
upload = client.uploads.upload(
    account_id=123,
    file_path="short.mp4",
    title="30 Days of Cooking Tips - Day 1 #shorts",
    tags=["shorts", "cooking", "tips"],
    privacy_status="public",
    thumbnail_path="thumbnail_day1.jpg",  # 1080×1920 JPEG
    extra={
        "playlistId": "PLxxxxxxxxxxxxxxxx",  # your playlist ID
        "categoryId": "26",                  # YouTube category: Howto & Style
        "madeForKids": False,
    }
)

print(upload)
# {"success": True, "data": {"uploadId": 790, "status": "pending"}}

# pip install google-api-python-client google-auth-oauthlib
import google_auth_oauthlib.flow
import googleapiclient.discovery
from googleapiclient.http import MediaFileUpload

# 1. OAuth 2.0: opens a browser to authorize your Google account
flow = google_auth_oauthlib.flow.InstalledAppFlow.from_client_secrets_file(
    "client_secret.json",
    scopes=["https://www.googleapis.com/auth/youtube.upload"],
)
credentials = flow.run_local_server(port=0)
youtube = googleapiclient.discovery.build("youtube", "v3", credentials=credentials)

# 2. videos.insert: put #Shorts in the title so YouTube classifies it as a Short
request = youtube.videos().insert(
    part="snippet,status",
    body={
        "snippet": {
            "title": "How to bake sourdough in 60s #Shorts",
            "description": "Quick recipe #Shorts",
            "tags": ["shorts", "baking"],
            "categoryId": "26",  # Howto & Style
        },
        "status": {"privacyStatus": "public", "selfDeclaredMadeForKids": False},
    },
    # Resumable upload: you own retries, token refresh & transcoding
    media_body=MediaFileUpload("short.mp4", chunksize=-1, resumable=True),
)
response = request.execute()
print(response["id"])  # the new video ID