PrintNow we are going to develop the main code for our tool that imports the gui_main.py and gui_newshapefile.py files, sets up the application, and connects the different GUI elements with event handler functions and functions that realize the actual functionality of the tool. We will organize the code into several modules. In particular, we will keep the functions that realize the main functionality, such as querying the different web portals, creating a new shapefile, etc. in a separate Python script file called core_functions.py . These functions are completely independent of the GUI of our tool and the few global variables we will need, so we might want to use them in other projects. Separating the project cleanly into GUI dependent and GUI independent code fosters reusability of the GUI independent code. Overall, the project will consist of the following Python files:
- gui_main.py – compiled version of gui_main.ui for setting up the GUI of the main window,
- gui_newshapefile.py – compiled version of gui_newshapefile.ui for setting up the GUI of the dialog box for creating a new shapefile,
- core_functions.py – contains definitions of functions for main functionality that are completely independent of GUI and global variables
- main.py – contains the event handler functions and the code for wiring up the GUI as well as setting up and running the application
In the following, we will focus on the code from main.py but we will start with a brief look at core_functions.py, so please download the file core_functions.py and open it so that you can read the code for the different functions. Most of the functions defined in the script should be rather easy to understand from the comments in the code and from your experience with using arcpy to work with shapefiles. Here is an overview of the functions with a few additional explanations:
- queryNominatim(query, limit=10, countryCodes=''): The purpose of this function is to query the Nominatim query interface of OSM for a query string and parameters for the limit of results returned and country code for the country to search in as discussed in Section 2.7.1. The code should be easy to understand: urllib.parse(…) is used to encode the query string to be used as part of a URL, before the final query URL is put together. The get(…) method of the requests package is used to run the actual query and the returned result is translated into JSON before being returned. Since no error handling is done in this function, we will have to deal with potential exceptions raised within the function in the code that calls this function.
- queryGeonames(query, maxRows = 10, username='', country='', featureClass=''): This function does the same as queryNominatim(...) but for GeoNames and for a different set of query parameters. Since GeoNames returns JSON code with the list of candidate features stored under the attribute 'geonames', we return json['geonames'] at the end.
- getStringFieldsForDescribeObject(desc): This is the first of a few auxiliary functions for getting information from shapefiles and layers. An arcpy.Describe object of a data set needs to be passed to it and it then returns a list of all editable string fields of that layer.
- getValidFieldsForShapefile(fileName): This function is used to get a list of editable string fields for a shapefile whose name is provided as a parameter. It relies on getStringFieldsForDescribeObject(…) to do most of the work but before that checks that the shapefile exists and is a Point vector data set. If not, it will return an empty list.
- createPointWGS1984Shapefile(fileName, fieldName): This function creates a new Point shapefile with the name provided as parameter, using WGS 1984 coordinates, and with a single additional string field whose name is also provided as a parameter.
- getPointLayersFromArcGIS(): This function is for getting a list of Layer objects for the layers currently open in ArcGIS Pro but only including Point layers.
- importArcpyIfAvailable(): This function returns True if arcpy is available for import, else False. It attempts to import arcpy within a try-except construct so that, if the operation fails, the resulting exception is caught and False is returned.
- runningAsScriptTool(): This function returns True if the program is run as a script tool inside ArcGIS, else False. This is accomplished by calling arcpy.mp.ArcGISProject("CURRENT") and catching the resulting exception if this operation fails, meaning the program is run as a standalone program outside of ArcGIS.
- webMapFromDictionaryList(features): This function produces and returns the HTML code for displaying the web map as part of the GUI. It gets the features that should be displayed on the map as parameter in the form of a list of dictionaries with name, lat, and lon attributes.
Now that you know the functions we have available for realizing the different operations that we will need, let’s develop the code for main.py together. Open a new file main.py in your IDE, then follow the steps listed on the next few pages.