When using StringIO, io.BytesIO or other file-like objects (such as Flask/werkzeug's file upload object), trying to upload via Blob.upload_from_file doesn't work because it attempts to find the size of the object using os.stat throwing a AttributeError: StringIO instance has no attribute 'fileno'. Passing in the size manually fixes this, but imo this inconsistency shouldn't burden the user as there are other ways than fileno to determine the size of a StringIO or io.BytesIO instance (seek, tell).

At any rate, the error message could be more helpful.