2.7.3.3: Step 3

We now add some code to initialize some global variables that we will need. Please add the following code directly under the comment “# initialize global variables”:

# dictionary mapping tabs from services tab widget to event handler functions 
queryHandler = { ui.nominatimTab: runNominatimQuery, ui.geonamesTab: runGeonamesQuery, ui.directInputTab: runDirectInput } 

# dictionary mapping tabs from add feature tab widget to event handler functions 
addFeaturesHandler = { ui.layerTab: addFeaturesToLayer, ui.shapefileTab: addFeaturesToShapefile, ui.csvTab: addFeaturesToCSV } 

result = []                     # global variable for storing query results as list of dictionaries 
arcValidLayers= {}              # dictionary mapping layer names to layer objects       

arcpyAvailable = False          # indicates whether is available for import 
runningAsScriptTool = False     # indicates whether script is run as script tool inside ArcGIS 

The first two variables defined, queryHandler and addFeaturesHandler, are dictionaries that contain the information of which event handler functions should be called when the “Run query” button and “Add features” button are clicked, respectively, depending on which of the tabs of the two different tab widgets are currently selected. Line 2, for instance, says that if currently the tab ui.nominatimTab is open in the Services section, then the function runNominatimQuery(…) should be called. So far we have not defined that function yet, hence, you will not be able to run the program at the moment but it shows you that functions in Python are treated like other kinds of objects, meaning they can, for instance, be stored in a dictionary. You will hear more about this in Lesson 3.

The other global variables we define in this piece of code are for keeping track of the results currently displayed in the Results list view widget of our GUI, of the currently open Point layers in ArcGIS when being run as a script tool, of whether the arcpy module is available, and of whether the program is being run as a script tool or not. We will add code to initialize the last two of these variables correctly in a moment