How to put 'args' into argparse.Argument in python

Question

For example, if I input "python prog.py create filename", the result should be create a file named "filename". But I don't know how to put "args" into defination of create. Could someone give me some advice ? This is code:

    import argparse
    import sys

    class ExecuteShell(object):

        def create(self, args):

        """create a file"""
        print 'xxxxxxxxxxx', args 

            #return args 

        def list(self, args):

        """ccccccc"""
        print args

            #return args

        def delete(self, args):

        """ddddddd"""
        print 'ddddddd'

            #return args

    class TestShell(object):

       def _find_actions(self, subparsers, actions_module, args):

            for attr in (action for action in dir(actions_module) if not action.startswith('__')):

            callback = getattr(actions_module, attr)

            desc = callback.__doc__ or ''

                subparser = subparsers.add_parser(attr, description=desc, add_help=False)

                subparser.add_argument('-h', '--help', action='help',
                                       help=argparse.SUPPRESS)    
                .......

       def main(self, args):

            parser = argparse.ArgumentParser()

            subparsers = parser.add_subparsers()

            a = ExecuteShell()

            subcommand_parser = self._find_actions(subparsers, a, args)

            (options, args) = parser.parse_known_args(args)

    if __name__ == "__main__":

        a = TestShell()
        a.main(sys.argv[1:])

Thanks a lot!

Are you mixing tabs and spaces in your source code file? You've mixed them in your example. Could you fix the indentation of your example? — Robᵩ
– Robᵩ, Commented Sep 17, 2013 at 3:50
Is this a port of an optparse example? Your use of parse_known_args suggests that. So you are creating subparsers that correspond (in name) to the methods (create, etc). But you don't define any arguments. I'd suggest creating a simpler parser modeled on the set_defaults() example of the sub-commands section of argparse documentation. Use the parser to parse the input, and then look in the returned Namespace for the create command and the file name. — hpaulj
– hpaulj, Commented Sep 17, 2013 at 16:21

Robᵩ · Accepted Answer · 2013-09-17 14:26:15Z

Within the framework you've outlined, I might implement it like the following program. The key items are:

parser.add_subparsers takes a dest argument. This lets you know which subparser was invoked.
add the an item to the subparser that collects the filenames (subparser.add_argument('files',...) below)
actually invoke the command subroutine (the getattr(a,options.command) ... line)

.

import argparse
import sys

class ExecuteShell(object):
    # This function demonstrates that you can put 
    # methods in ExecuteShell(), if you need to, 
    # without having them appear as command-line commands
    # simply by prepending an underscore.
    def _useful(self):
        """Useful method that ISNT a command."""
        return 3.14159

    def create(self, args):
        """create a file"""
        print 'xxxxxxxxxxx', args 

    def list(self, args):
        """ccccccc"""
        print args

    def delete(self, args):
        """ddddddd"""
        print 'ddddddd'

class TestShell(object):

   def find_actions(self, subparsers, actions_module, args):
        for attr in (action for action in dir(actions_module) if not action.startswith('_')):
            callback = getattr(actions_module, attr)
            desc = callback.__doc__ or ''
            subparser = subparsers.add_parser(attr, description=desc, help=desc)

            # This add_argument describes the positional argument, like so:
            #   'files' -- the result of matching this argument will be
            #              stored in `options.files`
            #   metavar='FILE' -- The help messages will use the word "FILE"
            #                     when describing this argument
            #   nargs='+' -- `narg` describes how many arguments this should
            #                match. The value `+` means "all of them, but at
            #                least one." 
            subparser.add_argument('files', metavar='FILE', nargs='+')

   def main(self, args):
        # setup parser
        parser = argparse.ArgumentParser()
        subparsers = parser.add_subparsers(dest='command')
        a = ExecuteShell()
        subcommand_parser = self.find_actions(subparsers, a, args)

        # Run parser
        args = parser.parse_args(args)

        # Run selected command
        # If we reach this statement, then:
        #    args.command is the command the user chose, 
        #       for example, 'create' or 'list'
        #    args.files is the list of arguments that followed 'create' or 'list'
        #    a is an instance of ExecuteShell
        #    getattr(a, args.command) is the attribute or method of `a`
        #       the name in `args.command`, for example, a.create or a.list
        #    getattr(a, args.command)(args.files) invokes that method,
        #       passing in the list of user arguments
        #    So, this line in effect might call `a.create(['file1', 'file2'])`
        getattr(a, args.command)(args.files)

if __name__ == "__main__":

    a = TestShell()
    a.main(sys.argv[1:])

First of all, thanks for your help. But I still have some questions, I hope you can help me to solve them. Question 1: What does "metavar='FILE', nargs='+'" mean? Question 2: Could you tell me what the mean of "def _useful(self)", it is not invoked... Thank you !
Asking a question again, "getattr(a, options.command)(options.files)" , how does it works ?

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