PYTHON: BUILDING GEOPROCESSING TOOLS

1. PYTHON: BUILDING GEOPROCESSING TOOLS David Wynne, Geri Miller

3. Why we build geoprocessing tools • Your work becomes part of the geoprocessing framework • Easy to access and run from within ArcGIS • Familiar look and feel • Make a mistake? Re-run from the previous result • Run from Python, ModelBuilder, as a service • Add to a tool bar • No UI programming

4. Geoprocessing Tool Commandments Thou shall … … have unique parameter names within the tool … keep the cost of validation to a minimum … always have an output, even if it must be derived … populate all output data elements within validation … not test the validity of any derived value within validation … have a coded value domain for every Boolean … test the function from a script, a model, a dialog, and the command line

5. Deconstructing a geoprocessing tool • A geoprocessing tool does three things • Defines parameters • Validates parameters • Executes source code

6. Turning Python code into geoprocessing tools Demo

7. Script tools vs Python toolboxes • Using Python, we can build tools in two ways: • Which do I use? • “A tool is a tool”

8. Parameters • Parameters are how you interact with a tool • Simple rules to guide behaviors • Does an input exist? • What are valid fields for this data? • Is this value an expected keyword?

9. Key parameter properties • Data type • Feature layers, raster layers, table views, … • String, Boolean, long, double, … • Direction • Input, output • Parameter type • Required, optional, derived

10. Parameter Dependencies (‘obtained from’) • Some data types are dependent on other parameters • Field, SQL Expression, Field Info provide little value on their own • Set a dependency to a different data type

11. Parameters - Symbology • Control the appearance of output by setting symbology • Set using a layer file either as : • Parameter property • Or in your source code • Important if you want to vary the symbology based on logical criteria

12. Filters • Filters are used to limit choices to acceptable values • For example: • A number between 1 and 10 • A string parameter with keywords • A file parameter that will only accept files with a .txt extension

13. Parameters - Defaults • Set a parameter default by value or by environment • Some data types match closely with geoprocessing environments • Can configure a parameter to use an environment by default

14. Parameter-izing a tool Demo

15. Parameters – Validation • As parameters are entered and modified, validation responds and interacts • Tools validate parameters in two ways • Basic (‘free’) validation, such as: • Does the input (or output) exist? • Is it the right data type? • Does this value match its filter? • Have all required parameters been supplied? • Additional rules and behavior you add

16. Validation • Provides more control • Parameter interaction • Calculate defaults • Enable or disable parameters • Setting parameter errors and messages • Defining output characteristics • Chain tools in ModelBuilder

17. Validation • Responding to: • value (or valueAsText) • altered • hasBeenValidated

18. A quick note about Python toolboxes and script tools

19. Validation: ModelBuilder • Describe outputs for chaining in ModelBuilder • Data variables in ModelBuilder includedescriptions of data • By updating the schema, subsequent tools can see pending changes prior to execution

20. Validation: Messages • Control over parameter messages • Evaluate system messages, and relax or change • Add more stringent errors based on your own criteria

21. Validation – Feature Layers • The type of a layer parameter changes depending if the input is a layer or feature class

22. Working with validation:Script tools and Python toolboxes Demo

23. Making your Python code work as a tool • Receiving parameters • Script tool – arcpy.GetParameter / GetParameterAsText • Python toolbox – parameter.value / parameter.valueAsText • Internal • Messages – arcpy.AddMessage / AddWarning / AddError … • Progressor (step or ‘cylon eye’) • Control actions (or not) after a cancellation • Derived values, if any, are pushed back to the tool

24. Cancelling toolsAdded at 10.4, Pro 1.1 • When a tool is cancelled… • ... by default, code will be cancelled after the current line • Using new environments, can respond to the cancellation • arcpy.env.autoCancelling • arcpy.env.isCancelled

25. Distributing your toolshttp://esriurl.com/extendingGP • Can ‘share’ a toolbox • Simply share the files or package a result • However, to have your tools blend seamlessly, distribute as a Python package • Are easily distributable • Toolboxes appear as System Toolboxes • Toolboxes become available through arcpy • Supports dialog side-panel help and localized messages • Requires specific structure

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27. Python at User Conference http://esriurl.com/PythonUC16