python argparse file extension checking

Question

can argparse be used to validate filename extensions for a filename cmd line parameter?

e.g. if i have a python script i run from the cmd line:

Answer 1

Define a custom function which takes the name as a string - split the extension off for comparison and just return the string if it's okay, otherwise raise the exception that argparse expects:

def valid_file(param):
    base, ext = os.path.splitext(param)
    if ext.lower() not in ('.csv', '.tab'):
        raise argparse.ArgumentTypeError('File must have a csv or tab extension')
    return param

And then use that function, such as:

parser = argparse.ArgumentParser()
parser.add_argument('filename', type=valid_file)