GEOG 485:
GIS Programming and Automation

4.6 Running any tool in the box


Sooner or later, you're going to have to include a geoprocessing tool in your script that you have never run before. It's possible that you've never even heard of the tool or run it from its GUI, let alone a script.

In other cases, you may know the tool very well, but your Python may be rusty, or you may not be sure how to construct all the necessary parameters.

The approach for both of these situations is the same. Here are some suggested steps for running any tool in the ArcGIS toolboxes using Python:

  1. Find the tool reference documentation. We've seen this already during the course. Each tool has its own topic in the Geoprocessing tool reference section of the ArcGIS Help. Open that topic and read it before you do anything else. Read the "Usage" section at the beginning to make sure that it's the right tool for you and that you are about to employ it correctly.
  2. Examine the parameters. Scroll down to the "Syntax" section of the topic and read which parameters the tool accepts. Note which parameters are required and which are optional, and decide which parameters your script is going to supply.
  3. In your Python script, create variables for each parameter. Note that each parameter in the "Syntax" section of the topic has a data type listed. If the data type for a certain parameter is listed as "String," you need to create a Python string variable for that parameter.

    Sometimes the translation from data type to Python variable is not direct. For example, sometimes the tool reference will say that the required variable is a "Feature Class." What this really means for your Python script is that you need to create a string variable containing the path to a feature class.

    Another example is if the tool reference says that the required data type is a "Long." What this means in Python is that you need to create a numerical variable (as opposed to a string) for that particular parameter.

    If you have doubts about how to create your variable to match the required data type, scroll down to the "Code Sample" in the tool reference topic. Try to find the place where the example script defines the variable you're having trouble with. Copy the patterns that you see in the example script and usually you'll be okay.

    Most of the commonly used tools have excellent example scripts, but others are hit or miss. If your tool of interest doesn't have a good example script, you may be able to find something on the Esri forums or a well-phrased Google search.

  4. Run the tool...with error handling. You can run your script without try/except blocks to catch any basic errors in the Interactive Window. If you're still not getting anything helpful, a next resort is to add the try/except blocks and put print arcpy.GetMessages() in the except block.

In Project 4 you'll get a chance to practice these skills to run a tool you previously haven't worked with in a script.