Using “schema.clone = True” on Python Toolbox Parameter?

Question

Cross-posted from GIS Stack Exchange. I have created a few different ArcGIS Python Toolboxes, but one thing I can't quite understand is when to apply "schema.clone = True" to a parameter. All of the examples I have seen show that I should be using it for derived parameters, as shown below, taken from Parameter Dependencies. # First parameter param0 = arcpy.Parameter( displayName="Input Features", name="in_features", datatype="GPFeatureLayer", parameterType="Required", direction="Input") # Third parameter param2 = arcpy.Parameter( displayName="Output Features", name="out_features", datatype="GPFeatureLayer", parameterType="Derived", direction="Output") param2.parameterDependencies = [param0.name] param2.schema.clone = True‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ However, when I try that on my code, it says the Tool is invalid when looking at it in Catalog. It gives me the following error when I click on the "Why..." button. Traceback (most recent call last): File "", line 481, in getParameterInfo AttributeError: 'NoneType' object has no attribute 'clone'‍‍‍ Here is what my code looks like. It works perfectly when I remove the schema clone line, which is confusing me. What exactly does that line do for me and when do I need it if it works fine without it? # Input Table input_table = arcpy.Parameter( displayName="Table or Feature Class", name="input_table", datatype=["GPFeatureLayer", "GPTableView"], parameterType="Required", direction="Input") params.append(input_table) # Derived Output Table output_table = arcpy.Parameter( displayName="Derived Output Table or Feature Class", name="output_table", datatype=["GPFeatureLayer", "GPTableView"], parameterType="Derived", direction="Output") output_table.parameterDependencies = [input_table.name] output_table.schema.clone = True params.append(output_table)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ I am currently running version 10.4 Someone over at GIS SE did some testing and led me to the following conclusions: * When I changed all the data types to ["GPFeatureLayer", "GPTableView"] it gave me the error. * I then changed all the data types to ["GPFeatureLayer"], and it still gave me the error. * Finally, I changed all the data types to "GPFeatureLayer", and it opened fine again. This tells me you can only have 1 data type, and it cannot be in brackets. So, how do you handle cases where you need multiple possible input types? That seems like a pretty common use case. Or do you simply not need to include the schema clone line at all?

DanPatterson_Retired · Answer

According to this, it makes a clone of the first dependent parameter, which must be throwing a None (NoneType) and expects only one value as input, perhaps tossing everything if there is more than one

Schema—Help | ArcGIS Desktop You will have to check the details

ADDENDUM

type
(Read Only)
The schema type: Feature, Table, Raster, or Container (for workspaces and feature datasets).
String

perhaps the type is expecting one, and container for the latter

DanPatterson_Retired · Answer

more info here /blogs/dan_patterson/2016/08/14/script-formatting

Justin_P · Answer

Thanks Dan_Patterson. I was looking for one but never saw that.