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
12Function 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.
