efficient and complete input check for command line argument and option with python

Question

I am developing cli with python version 2.4.3. i want to have the input exception check. The following is part of the code. With this code, I can type

addcd -t 11 

and if I type

addcd -t str_not_int

or

addcd -s 3

I will catch the error of wrong type argument and wrong option. However, it is not sufficient. e.g.

addcd s 11

or

addcd s a 

then the optparse cannot detect this kind of misinput.

to eliminate the case like "addcd s a 11 21", I add something by checking number of argument, but I do not know if it is the right way.

So, how can I implement a thorough/efficient input check for CLI?

class OptionParsingError(RuntimeError):
    def __init__(self, msg):
        self.msg = msg

class OptionParsingExit(Exception):
    def __init__(self, status, msg):
        self.msg = msg
        self.status = status

class ModifiedOptionParser(optparse.OptionParser):
    def error(self, msg):
        raise OptionParsingError(msg)

    def exit(self, status=0, msg=None):
        raise OptionParsingExit(status, msg)

class CDContainerCLI(cmd.Cmd):
    """Simple CLI """
    def __init__(self):
        """ initialization """ 
        cmd.Cmd.__init__(self) 
        self.cdcontainer=None

    def addcd(self, s):
        args=s.split()
        try:
            parser = ModifiedOptionParser()
            parser.add_option("-t", "--track", dest="track_number", type="int",
               help="track number")
            (options, positional_args) = parser.parse_args(args)
        except OptionParsingError, e:
            print 'There was a parsing error: %s' % e.msg
            return
        except OptionParsingExit, e:
            print 'The option parser exited with message %s and result code %s' % (e.msg, e.status)
        return
        if len(args) != 4:
            print "wrong number of inputs"
            return

        cd_obj= CD()
        cd_obj.addCD(options.track_number, options.cd_name)

Answer 1

First, read this http://docs.python.org/library/optparse.html#terminology.

You're not following the optparse rules for options. If you don't follow the rules, you cannot use this library.

Specifically.

addcd s 11

or

addcd s a 

Are not legal options. No "-". No "--". Why no "-"?

"then it cannot detect."

Cannot detect what? Cannot detect that they're present? Of course not. They're not legal options.

Cannot detect that the option parameters are the right type? Of course not. They're not legal options to begin with.

---

eliminate the case of "addcd s a 11 21"

Since none of that looks like legal options, then optparse can't help you. Those aren't "options".

Those are "arguments". They will be found in the variable positional_args. However, you're not using that variable. Why not?

---

Indeed, this code

    return
    if len(args) != 4:
        print "wrong number of inputs"
        return

Makes no sense at all. After return no statement can be executed. Why write code after a return?

Why check the len of args after parsing args? It's already parsed, it's too late to care how long it was.