validation.py

class ToolValidator:
    # Class to add custom behavior and properties to the tool and tool parameters.

    def __init__(self):
        # set self.params for use in other function
        self.params = arcpy.GetParameterInfo()

    def updateMessages(self):
        # Customize messages for the parameters.
        # This gets called after standard validation.
        shapetype = arcpy.Describe(self.params[5]).shapeType.lower()
        if shapetype == "polygon" or shapetype == "line":
            self.params[5].setErrorMessage("Should be a point shapefile.")
        return

    def initializeParameters(self):
        # Customize parameter properties.
        # This gets called when the tool is opened.
        return

    def updateParameters(self):
        # Modify parameter values and properties.
        # This gets called each time a parameter is modified, before
        # standard validation.
        return

    # def isLicensed(self):
    #     # set tool isLicensed.
    # return True

    # def postExecute(self):
    #     # This method takes place after outputs are processed and
    #     # added to the display.
    # return