I keep getting a "$return binding returned a non-None value" error. I can't figure it out?

[epmck]

I am trying to do a Durable Entity function locally, and I started trying to create my own. Every time I did I would get this error: Exception: RuntimeError: function 'DurableFunctionsEntityPy' without a $return binding returned a non-None value

So I finally found this project and I thought it would help me figure out what I'm doing wrong, but even when I clone this repo and try running it, I'm getting the same error. I swear there is no "return" in my Entity function. What is causing this issue? Please help, this is driving me crazy!

@counter@myCounter: Function 'counter (Entity)' failed with an error. Reason: Internal error: Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcException: Result: Failure
Exception: RuntimeError: function 'Counter' without a $return binding returned a non-None value

[ConnorMcMahon]

Can you share your function.json content with us? Given the error message it appears that this is the likely culprit.

[davidmrdavid]

Thanks for reaching out @epmck! Unless I'm mistaken, I believe we discussed this issue on Twitter about a week ago. In any case, I finally got around patching the sample to include this fix here: #296

The fix should be merged soon!

[davidmrdavid]

Fix was merged! Closing this issue. Please re-open if the issue continues on your end. Thanks! :)

[FaCoffee1984]

@davidmrdavid I see a similar error with my Python Durable Function (function chaining). The logs say:
RuntimeError: function 'function-name' without a $return binding returned a non-None value.

It sounds like this has been addressed with a fix in 2021, but why is it happening to me? As you can see, I have an output biding called outputDocument which my function is using to write data to a Cosmos DB, so I struggle to make sense of that error message. Does this have anything to do with the host.json file and the bundle version, perhaps?

My function.json:

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "data-from-previous-function",
      "type": "activityTrigger",
      "direction": "in"
    },
    {
      "type": "cosmosDB",
      "direction": "in",
      "name": "encoding",
      "databaseName": "database-name",
      "collectionName": "collection-name",
      "createIfNotExists": "true",
      "connectionStringSetting": "cosmos_conn_string",
      "partitionKey": "id",
      "sqlQuery": "SELECT TOP 1 * FROM c ORDER BY c._ts desc"
    },
    {
      "type": "cosmosDB",
      "direction": "out",
      "name": "outputDocument",
      "databaseName": "database-name",
      "collectionName": "collection-name",
      "createIfNotExists": "true",
      "connectionStringSetting": "cosmos_conn_string",
      "partitionKey": "id"
    }
  ]
}

My host.json:

{
  "version": "2.0",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[2.*, 3.0.0)"
  }
}

My __init__.py:

def main(data_from_previous_function, encoding, outputDocument: func.Out[func.Document]) -> str:

    inputDocument = data_from_previous_function.copy()

    #Logging
    if inputDocument:
        logging.info('Document id: %s', inputDocument['id'])

    #Read some values from Cosmos DB
    encodings = encoding[0].data 

    #Modify values in json file
    output_data = modify(inputDocument, encodings) # The result is a valid json file 
    
    # Send output to Cosmos DB
    outputDocument.set(func.Document.from_dict(output_data))    

    return output_data # Return data to Orchestrator for the next processing step in the function chain

[thec0dewriter]

Hello @FaCoffee1984
I've been facing this issue also for a few days, but I can't reproduce locally. I've opened a new ticket for it: #399

[davidmrdavid]

@FaCoffee1984, @thec0dewriter:

Thanks for your report. I have received a few of these over the past day, and it seems that some automatic upgrade may have caused a regression. I'm actively investigating this, so please subscribe to the following thread for updates: #401