I want Python argparse to throw an exception rather than usage

Question

I don't think this is possible, but I want to handle exceptions from argparse myself.

For example:

import argparse parser = argparse.ArgumentParser() parser.add_argument('--foo', help='foo help', required=True) try:     args = parser.parse_args() except:     do_something() 

When I run it:

$ myapp.py usage: myapp --foo foo myapp: error: argument --foo is required 

But I want it to fall into the exception instead.

Answer 1

You can subclass ArgumentParser and override the error method to do something different when an error occurs:

class ArgumentParserError(Exception): pass  class ThrowingArgumentParser(argparse.ArgumentParser):     def error(self, message):         raise ArgumentParserError(message)  parser = ThrowingArgumentParser() parser.add_argument(...) ... 

Answer 2

in my case, argparse prints 'too few arguments' then quit. after reading the argparse code, I found it simply calls sys.exit() after printing some message. as sys.exit() does nothing but throws a SystemExit exception, you can just capture this exception.

so try this to see if it works for you.

    try:         args = parser.parse_args(args)     except SystemExit:         .... your handler here ...         return