python argparse: How can I display help automatically on error?
Pergunta
Currently when I enter invalid options or omit positional arguments, argparse kicks me back to the prompt and displays the usage for my app. This is ok, but I would rather automatically display the full help listing (that explains the options, etc) than require the user to type
./myscript.py -h
Thanks!
Jamie
Solução
This thread over at Google groups has the following code snippet which seems to do the trick (modified slightly).
class DefaultHelpParser(argparse.ArgumentParser):
def error(self, message):
sys.stderr.write('error: %s\n' % message)
self.print_help()
sys.exit(2)
Outras dicas
To print help you might want to use: print_help
function on ArgumentParser
instance
parser = argparse.ArgumentParser()
(...)
parser.print_help()
To print help message on error you need to create own subclass of ArgumentParser
instance, that overrides error()
method. For example like that:
class MyParser(argparse.ArgumentParser):
def error(self, message):
sys.stderr.write('error: %s\n' % message)
self.print_help()
sys.exit(2)
When this parser encounters unparseable argument line it will print help.