What is the type of the `messages` parameter in a Python toolbox's `execute` method?

Question

I've modified the `execute` method of a python toolbox thusly:

def execute(self, parameters: list[arcpy.Parameter], messages):

The type hint for the `parameters` parameter allows VS Code to provide useful IDE behavior like code completion and such.  I'd like to do the same for the `messages` parameter, but I cannot find the type to put there in Esri doc.  I've tried this . . .

messages.addMessage(f"---{type(messages)}---")

but that simply tells me 'geoprocessing messages object', which doesn't get me any closer to the actual class name of that object.  The doc for this is also curiously silent on the matter.  Help?

MortenBackNielsen · Answer

Another suggestion could be to use the Geoprocessor class in arcpy

from arcpy import Geoprocessor as ArcGISMessage

RogerDunnGIS · Answer

As I said, the underlying class could be different depending on where the tool is running and its environment.  Your main concern is know which class represents the messages parameter when the tool is running from inside ArcGIS Pro as a Tool in a Toolbox.

Since Python is written in C (isn't it?), I wonder if a developer like Esri can make a non-Python class that implements the required methods and properties.  I'm pretty sure that class developers can hide the underlying class by implementing special __methods__ and Esri took this liberty.

dan.narsavage_IDWR · Answer

Sure enough this informal interface . . .

class EsriMessagesSecretInterface:
    """
    Informal interface to allow VS Code to do useful things with the 'messages' parameter of python toolboxes
    https://pro.arcgis.com/en/pro-app/latest/arcpy/geoprocessing_and_python/writing-messages-in-a-python-toolbox.htm
    """
    def addMessage(self, message: str) -> None:
        """An informative message is added to the tool's messages."""
        pass

def addWarningMessage(self, message: str) -> None:
        """A warning message is added to the tool's messages."""
        pass

def addErrorMessage(self, message: str) -> None:
        """An error message is added to the tool's messages."""
        pass

def addIDMessage(self, message_type, message_ID, add_argument1=None, add_argument2=None) -> None:
        """
        A message of any type is added using geoprocessing message codes.
        I don't really know what this means.
        """
        pass

def addGPMessages(self) -> None:
        """
        Messages from the last geoprocessing tool run are added to the tool's messages.
        I don't really know what this means.
        """
        pass

. . . coupled with this method declaration . . .

def execute(self, parameters: list[arcpy.Parameter], messages: EsriMessagesSecretInterface):

. . . yields the behavior I want in VSCode.  Thanks!

. . . But I'd still prefer just to use the type that Esri made.  😄