The isLicensed method is an optional method that can be used to check if a tool in a Python toolbox is licensed to execute. It can be used to restrict the tool from being run if the appropriate licenses and extensions required to run other geoprocessing tools used by the Python toolbox tool are not available.
If the isLicensed method returns False, the tool cannot be executed. If the method returns True or the method is not used, the tool can be executed.
"""Allow the tool to execute, only if the ArcGIS 3D Analyst extension
if arcpy.CheckExtension("3D") != "Available":
return False # tool cannot be executed
return True # tool can be executed