• Package Name: azure-storage-blob
• Package Version: latest
• Operating System: macOS
• Python Version: Python 3.9

The async BlobClient class uses BlobClient (sync) as a mixin. The class method factories for instantiating the client, such as from_connection_string, from_blob_url have a type annotated return type as BlobClient, which is invalid:

https://github.com/Azure/azure-sdk-for-python/blob/main/sdk/storage/azure-storage-blob/azure/storage/blob/_blob_client.py#L203-L206

The return type should be cls, using a TypeVar[T]. This ends up causing issues with type systems when you use the methods.

This simple example demonstrates the issue

from typing import Any, Dict
from azure.storage.blob.aio import (
    BlobClient,
)


async def download_blob(blob_url: str) -> Any:
    blob_client = BlobClient.from_blob_url(blob_url)  # Has type BlobClient instead of AsyncBlobClient
    response = await (await blob_client.download_blob()).readall()  # Works but raises type errors
    return response

Any type tool then causes issue because it thinks that blob_client is the sync client and not the async client.