[BUG] Inconsistent typing of Python Azure Function blob-bound parameter

[shwars]

When input parameter of Azure Function that is bound to Blob is typed as bytes, the actual type is str.

Official documentation states that the parameter should be typed as InputStream. This is the default when no typing is specified. However, we can specify str type and get the string. If we specify the type of input variable as bytes, the actual type is also str, which makes using the raw binary data difficult.

Azure Functions in C# support many different types, which makes development much more convenient. It would be nice to have the same functionality in Python to be consistent.

Proposed solutions:

• Allow to specify bytes as input type, fix incorrect typing and add this to documentation
• Throw type error exception if typing is specified incorrectly

Investigative information

• Core Tools version: 3.0.2852

Repro steps

Create the following http-triggered Azure Function:

Code

import logging
import azure.functions as func

def main(inblb: bytes , req: func.HttpRequest) -> func.HttpResponse:
    logging.info(f"Type of input object is {type(inblb)}")
    return func.HttpResponse(f"Type of input object is {type(inblb)}",status_code=200)

inblb is bound to Azure Blob Storage:

function.json

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "$return"
    },
    {
      "type": "blob",
      "direction": "in",
      "name": "inblb",
      "path": "thecontainer/thefile",
      "connection": "demoazfuncstorage_STORAGE"
    }
  ]
}

Expected behavior

Either one of:

• [suggested] Type of input object is bytes
• Exception is thrown to indicate incorrect typing

Actual behavior

Type of input object is str

Known workarounds

Use func.InputStream as type of blob-bound parameter, and obtain the content of blob using read() method.

[shwars]

The actual type of the parameter is determined by dataType in function.json binding definition, and Python type declaration (str or bytes) is ignored. Ideally, an error or warning should be issued if the variable is typed incorrectly.

[vrdmr]

We should discuss if we should explicitly add dataType to Python's BlobTrigger template.

/cc @stefanushinardi, @anirudhgarg

[vrdmr]

Doc update PR out: MicrosoftDocs/azure-docs#64747

[vrdmr]

MicrosoftDocs/azure-docs#64747 is now merged and this issue can be closed. Thanks, @shwars for bringing this up and adding the documentation 👍🏼