Module 10 - Creating Custom Tools

This week we created a custom tool using a Python based script. The script simply clips several files at once to a single defined extent. Incidentally there are several differences between a script and a tool, the most notable being:

• stand-alone scripts need to work with hard-coded file paths and variables
• stand alone scripts tend to be run within an IDE
• tools do not need to have hard-coded file paths and variables - in fact, that is usually not preferred
• the use of tools within ArcGIS does not require any knowledge of Python whatsoever
• while both scripts and tools can be shared, tools are more easily shared because they are not generally tied to any specific file paths

The first step in creating a custom tool is in making sure that there is a toolbox created within which to put it. Next one adds a script to the toolbox - ArcGIS provides an add script wizard where the majority of the script-to-tool conversion takes place. Parameters for the tool can be defined at this time - for the assignment these were the input and output file paths, and also the clip boundary and input features. We had also set up specific file paths for the input and output parameters - but it would be just as easy to create the tool without these being completely defined. An example of the final tool is shown below.

The multi-clip tool opening screen.

In order to finalize the tool the script needs to be modified so that it will work within a tool environment. Our original script had referenced specific datasets and file paths and so needed to be a bit more flexible. This was accomplished by using the arcpy.GetParameters() function to replace specific file paths and variable dataset locations. The arcpy.AddMessage() function was used to convert all Python interactive window print statements to printed text within the geoprocessing results window, as shown in the screenshot of the tool results below.

Screenshot of the geoprocessing results window after running the multi-clip tool.

A fun little feature within ArcGIS is that one can change the code and the tool within ArcCatalog - the Python IDE does not need to be opened! A downside of this is that the code is instead edited within notepad, so any mistakes in syntax are not as easily caught. For this reason it seems to me that code edits within ArcCatalog should be kept to a minimum - meaning that it's best to have a complete code (or nearly so) when first creating a custom tool.