testing

Python GIS tools with a long processing-time benefit from a testing mode, which quickly verifies the tool functionality. Usually this is achieved by using default parameter values and/or a small test-dataset.

The code below implements a test option into a Python tool, leveraging the argparse subparser functionality.

From Command Line, the tool can be run in either a test (running with default parameters) or full mode (running with user-provided parameters).

import argparse


def model_core(args): 
    """function with core functionality. Takes args Namespace as single argument"""
    print(args.a * args.b)


def f_test(f_args):
    """run model core with default arguments for testing"""
    print('testing with default values")
    model_core(f_args)


def f_full(f_args):
    """run model core with user defined arguments"""
    print('running with user provided values")
    model_core(f_args)

parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers()  

parser_test = subparsers.add_parser('test')  # Create testing sub-parser
parser_test.set_defaults(func=f_test, a=10, b=20)  # Tie sub-parser to a function

parser_full = subparsers.add_parser('full')  # Create full function sub-parser
parser_full.add_argument('a', type=int)  # Add positional arguments
parser_full.add_argument('b', type=int)  
parser_full.set_defaults(func=f_full)  # Tie sub-parser to a function

args=parser.parse_args()  # Parse arguments from command line
args.func(args)  # Exectute the function associated with the enabled sub-parser

> python my_model.py test
testing with default values
200
> python my_model.py full 2 6
running with user provided values
12

Function and sub-parser are coupled using the set_defaults method. The function is called, and args provided as argument, using the args.func(args) method. For the full sub-parser, all required attributes are provided by the user. The test sub-parser has default values specified, again with the set_defaults method. The model_core function accepts a single Namespace as argument and extracts attributes as parameters where needed.