Event Grid output binding does not work on Python

[johndowns]

In the process of updating the documentation for the Event Grid output binding (see this PR), I discovered that the output binding does not work correctly with Python functions. It does work correctly for .NET and Node.js. (Note I have opened a separate issue to log that this doesn't work for Java either.)

• I used this function.json and this function code.
• When I ran the function, I got this error:

Result: Failure
Exception: FunctionLoadError: cannot load the MyFunction function: Python return annotation "EventGridEvent" does not match binding type "eventGrid"
Stack:   File "/azure-functions-host/workers/python/3.7/LINUX/X64/azure_functions_worker/dispatcher.py", line 245, in _handle__function_load_request
    function_id, func, func_request.metadata)
  File "/azure-functions-host/workers/python/3.7/LINUX/X64/azure_functions_worker/functions.py", line 241, in add_function
    f'Python return annotation "{return_pytype.__name__}" '

• I wonder if the issue is that the binding extension bundle does not include a reference to the eventGrid output binding (only to eventGridTrigger) - I have no idea how this works though, and if it's sufficient to simply put a PR adding that one line to the extensions.json or if something more needs to be done to wire it up.

[pragnagopa]

@Hazhzeng - can you please take a look? Also, add E2E test for event grid if not exists

[pragnagopa]

@johndowns - For Java, please see: https://github.com/Azure/azure-functions-java-worker/blob/dev/endtoendtests/src/main/java/com/microsoft/azure/functions/endtoend/EventGridTriggerTests.java for an example. If it still does not work, please open a separate issue here: https://github.com/Azure/azure-functions-java-worker/

[johndowns]

@johndowns - For Java, please see: https://github.com/Azure/azure-functions-java-worker/blob/dev/endtoendtests/src/main/java/com/microsoft/azure/functions/endtoend/EventGridTriggerTests.java for an example. If it still does not work, please open a separate issue here: https://github.com/Azure/azure-functions-java-worker/

Thanks. That test doesn't invoke the output binding, just the trigger, so my original point stands. I will open a new issue on the other repo and adjust the description of this issue to restrict it to Python.

[Hazhzeng]

Yea, I think this issue is more of a feature request. According to the documents, Python and Java does not support Output Binding for Event Grid yet.

I will discuss with my team and update you once this is ready.

[johndowns]

@Hazhzeng yes, I wrote that part of the document :) I spoke to Jeff Hollan about this and he asked me to open this issue as the bindings should be consistent across languages.