I have been working on a Python toolbox which contains 6 parameters. I am a little lost on all of the different data types available in ArcMap (it seems like there's *hundreds* of them!). However, one of the input parameters has a file extension of .shp (shapefile). I have always used the GPFeatureLayer data type and it has always worked for everything else I hope to do with my tool, although I don't completely understand why. I have only been doing my testing with point shapefiles for the time being. 

What I would ultimately hope to do is check if the user has entered a shapefile that is not a point (or a collection of points). If it is not a point, throw a warning to the user, but still allow them to use the tool. From what I understand, you can check the shape type by utilizing the [Describe() class][1]. However, when I attempt to pass my parameter into Describe (in order to return a Describe object), ArcMap throws an error:

![enter image description here][2]

Here is how I define the parameter I am focusing on:

    def getParameterInfo(self):
        """Define parameter definitions"""

        # First parameter = layer with customized features
        param0 = arcpy.Parameter(
            displayName = "Source layer with customized features",
            name = "source",
            datatype = "GPFeatureLayer",
            parameterType = "Required",
            direction = "Input")

And I was hoping to throw the warning in the updateParameters() method:

    def updateParameters(self, parameters):
        if parameters[2].value == True:
            parameters[3].enabled = True
            parameters[4].enabled = True
            parameters[5].enabled = True
            
        else:       
            parameters[3].enabled = False
            parameters[4].enabled = False
            parameters[5].enabled = False       
        
        describe = arcpy.Describe(parameters[0])
        if describe.shapeType == 'Point':
            arcpy.AddWarning('Warning: This is a point shapefile')

Any ideas as to why I am getting this error? Am I using the correct data type? I have tried using other data types for this parameter, such as DEFeatureClass, GPPoint, and DEShapefile, but I received the following error if I tried adding my shapefile in as my parameter:

![enter image description here][3]

The error was the same regardless of which of the three I used. Any assistance on this would be appreciated. 

  [1]: http://resources.arcgis.com/en/help/main/10.1/index.html#/Describe/018v00000066000000/
  [2]: https://i.sstatic.net/6TuE9.jpg
  [3]: https://i.sstatic.net/GeQxZ.jpg