argparse.py

# -*- coding: utf-8 -*-

# Copyright © 2006-2009 Steven J. Bethard <steven.bethard@gmail.com>.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may not
# use this file except in compliance with the License. You may obtain a copy
# of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

"""Command-line parsing library

This module is an optparse-inspired command-line parsing library that:

    - handles both optional and positional arguments
    - produces highly informative usage messages
    - supports parsers that dispatch to sub-parsers

The following is a simple usage example that sums integers from the
command-line and writes the result to a file::

    parser = argparse.ArgumentParser(
        description='sum the integers at the command line')
    parser.add_argument(
        'integers', metavar='int', nargs='+', type=int,
        help='an integer to be summed')
    parser.add_argument(
        '--log', default=sys.stdout, type=argparse.FileType('w'),
        help='the file where the sum should be written')
    args = parser.parse_args()
    args.log.write('%s' % sum(args.integers))
    args.log.close()

The module contains the following public classes:

    - ArgumentParser -- The main entry point for command-line parsing. As the
        example above shows, the add_argument() method is used to populate
        the parser with actions for optional and positional arguments. Then
        the parse_args() method is invoked to convert the args at the
        command-line into an object with attributes.

    - ArgumentError -- The exception raised by ArgumentParser objects when
        there are errors with the parser's actions. Errors raised while
        parsing the command-line are caught by ArgumentParser and emitted
        as command-line messages.

    - FileType -- A factory for defining types of files to be created. As the
        example above shows, instances of FileType are typically passed as
        the type= argument of add_argument() calls.

    - Action -- The base class for parser actions. Typically actions are
        selected by passing strings like 'store_true' or 'append_const' to
        the action= argument of add_argument(). However, for greater
        customization of ArgumentParser actions, subclasses of Action may
        be defined and passed as the action= argument.

    - HelpFormatter, RawDescriptionHelpFormatter, RawTextHelpFormatter,
        ArgumentDefaultsHelpFormatter -- Formatter classes which
        may be passed as the formatter_class= argument to the
        ArgumentParser constructor. HelpFormatter is the default,
        RawDescriptionHelpFormatter and RawTextHelpFormatter tell the parser
        not to change the formatting for help text, and
        ArgumentDefaultsHelpFormatter adds information about argument defaults
        to the help.

All other classes in this module are considered implementation details.
(Also note that HelpFormatter and RawDescriptionHelpFormatter are only
considered public as object names -- the API of the formatter objects is
still considered an implementation detail.)
"""

__version__ = '1.1a1'
__all__ = [
    'ArgumentParser',
    'ArgumentError',
    'Namespace',
    'Action',
    'FileType',
    'HelpFormatter',
    'RawDescriptionHelpFormatter',
    'RawTextHelpFormatter',
    'ArgumentDefaultsHelpFormatter',
]


import copy as _copy
import os as _os
import re as _re
import sys as _sys
import textwrap as _textwrap

from gettext import gettext as _

try:
    _set = set
except NameError:
    from sets import Set as _set

try:
    _basestring = basestring
except NameError:
    _basestring = str

try:
    _sorted = sorted
except NameError:

    def _sorted(iterable, reverse=False):
        result = list(iterable)
        result.sort()
        if reverse:
            result.reverse()
        return result


def _callable(obj):
    return hasattr(obj, '__call__') or hasattr(obj, '__bases__')

# silence Python 2.6 buggy warnings about Exception.message
if _sys.version_info[:2] == (2, 6):
    import warnings
    warnings.filterwarnings(
        action='ignore',
        message='BaseException.message has been deprecated as of Python 2.6',
        category=DeprecationWarning,
        module='argparse')


SUPPRESS = '==SUPPRESS=='

OPTIONAL = '?'
ZERO_OR_MORE = '*'
ONE_OR_MORE = '+'
PARSER = 'A...'
REMAINDER = '...'

# =============================
# Utility functions and classes
# =============================

class _AttributeHolder(object):
    """Abstract base class that provides __repr__.

    The __repr__ method returns a string in the format::
        ClassName(attr=name, attr=name, ...)
    The attributes are determined either by a class-level attribute,
    '_kwarg_names', or by inspecting the instance __dict__.
    """

    def __repr__(self):
        type_name = type(self).__name__
        arg_strings = []
        for arg in self._get_args():
            arg_strings.append(repr(arg))
        for name, value in self._get_kwargs():
            arg_strings.append('%s=%r' % (name, value))
        return '%s(%s)' % (type_name, ', '.join(arg_strings))

    def _get_kwargs(self):
        return _sorted(self.__dict__.items())

    def _get_args(self):
        return []


def _ensure_value(namespace, name, value):
    if getattr(namespace, name, None) is None:
        setattr(namespace, name, value)
    return getattr(namespace, name)


# ===============
# Formatting Help
# ===============

class HelpFormatter(object):
    """Formatter for generating usage messages and argument help strings.

    Only the name of this class is considered a public API. All the methods
    provided by the class are considered an implementation detail.
    """

    def __init__(self,
                 prog,
                 indent_increment=2,
                 max_help_position=24,
                 width=None):

        # default setting for width
        if width is None:
            try:
                width = int(_os.environ['COLUMNS'])
            except (KeyError, ValueError):
                width = 80
            width -= 2

        self._prog = prog
        self._indent_increment = indent_increment
        self._max_help_position = max_help_position
        self._width = width

        self._current_indent = 0
        self._level = 0
        self._action_max_length = 0

        self._root_section = self._Section(self, None)
        self._current_section = self._root_section

        self._whitespace_matcher = _re.compile(r'\s+')
        self._long_break_matcher = _re.compile(r'\n\n\n+')

    # ===============================
    # Section and indentation methods
    # ===============================
    def _indent(self):
        self._current_indent += self._indent_increment
        self._level += 1

    def _dedent(self):
        self._current_indent -= self._indent_increment
        assert self._current_indent >= 0, 'Indent decreased below 0.'
        self._level -= 1

    class _Section(object):

        def __init__(self, formatter, parent, heading=None):
            self.formatter = formatter
            self.parent = parent
            self.heading = heading
            self.items = []

        def format_help(self):
            # format the indented section
            if self.parent is not None:
                self.formatter._indent()
            join = self.formatter._join_parts
            for func, args in self.items:
                func(*args)
            item_help = join([func(*args) for func, args in self.items])
            if self.parent is not None:
                self.formatter._dedent()

            # return nothing if the section was empty
            if not item_help:
                return ''

            # add the heading if the section was non-empty
            if self.heading is not SUPPRESS and self.heading is not None:
                current_indent = self.formatter._current_indent
                heading = '%*s%s:\n' % (current_indent, '', self.heading)
            else:
                heading = ''

            # join the section-initial newline, the heading and the help
            return join(['\n', heading, item_help, '\n'])

    def _add_item(self, func, args):
        self._current_section.items.append((func, args))

    # ========================
    # Message building methods
    # ========================
    def start_section(self, heading):
        self._indent()
        section = self._Section(self, self._current_section, heading)
        self._add_item(section.format_help, [])
        self._current_section = section

    def end_section(self):
        self._current_section = self._current_section.parent
        self._dedent()

    def add_text(self, text):
        if text is not SUPPRESS and text is not None:
            self._add_item(self._format_text, [text])

    def add_usage(self, usage, actions, groups, prefix=None):
        if usage is not SUPPRESS:
            args = usage, actions, groups, prefix
            self._add_item(self._format_usage, args)

    def add_argument(self, action):
        if action.help is not SUPPRESS:

            # find all invocations
            get_invocation = self._format_action_invocation
            invocations = [get_invocation(action)]
            for subaction in self._iter_indented_subactions(action):
                invocations.append(get_invocation(subaction))

            # update the maximum item length
            invocation_length = max([len(s) for s in invocations])
            action_length = invocation_length + self._current_indent
            self._action_max_length = max(self._action_max_length,
                                          action_length)

            # add the item to the list
            self._add_item(self._format_action, [action])

    def add_arguments(self, actions):
        for action in actions:
            self.add_argument(action)

    # =======================
    # Help-formatting methods
    # =======================
    def format_help(self):
        help = self._root_section.format_help()
        if help:
            help = self._long_break_matcher.sub('\n\n', help)
            help = help.strip('\n') + '\n'
        return help

    def _join_parts(self, part_strings):
        return ''.join([part
                        for part in part_strings
                        if part and part is not SUPPRESS])

    def _format_usage(self, usage, actions, groups, prefix):
        if prefix is None:
            prefix = _('usage: ')

        # if usage is specified, use that
        if usage is not None:
            usage = usage % dict(prog=self._prog)

        # if no optionals or positionals are available, usage is just prog
        elif usage is None and not actions:
            usage = '%(prog)s' % dict(prog=self._prog)

        # if optionals and positionals are available, calculate usage
        elif usage is None:
            prog = '%(prog)s' % dict(prog=self._prog)

            # split optionals from positionals
            optionals = []
            positionals = []
            for action in actions:
                if action.option_strings:
                    optionals.append(action)
                else:
                    positionals.append(action)

            # build full usage string
            format = self._format_actions_usage
            action_usage = format(optionals + positionals, groups)
            usage = ' '.join([s for s in [prog, action_usage] if s])

            # wrap the usage parts if it's too long
            text_width = self._width - self._current_indent
            if len(prefix) + len(usage) > text_width:

                # break usage into wrappable parts
                part_regexp = r'\(.*?\)+|\[.*?\]+|\S+'
                opt_usage = format(optionals, groups)
                pos_usage = format(positionals, groups)
                opt_parts = _re.findall(part_regexp, opt_usage)
                pos_parts = _re.findall(part_regexp, pos_usage)
                assert ' '.join(opt_parts) == opt_usage
                assert ' '.join(pos_parts) == pos_usage

                # helper for wrapping lines
                def get_lines(parts, indent, prefix=None):
                    lines = []
                    line = []
                    if prefix is not None:
                        line_len = len(prefix) - 1
                    else:
                        line_len = len(indent) - 1
                    for part in parts:
                        if line_len + 1 + len(part) > text_width:
                            lines.append(indent + ' '.join(line))
                            line = []
                            line_len = len(indent) - 1
                        line.append(part)
                        line_len += len(part) + 1
                    if line:
                        lines.append(indent + ' '.join(line))
                    if prefix is not None:
                        lines[0] = lines[0][len(indent):]
                    return lines

                # if prog is short, follow it with optionals or positionals
                if len(prefix) + len(prog) <= 0.75 * text_width:
                    indent = ' ' * (len(prefix) + len(prog) + 1)
                    if opt_parts:
                        lines = get_lines([prog] + opt_parts, indent, prefix)
                        lines.extend(get_lines(pos_parts, indent))
                    elif pos_parts:
                        lines = get_lines([prog] + pos_parts, indent, prefix)
                    else:
                        lines = [prog]

                # if prog is long, put it on its own line
                else:
                    indent = ' ' * len(prefix)
                    parts = opt_parts + pos_parts
                    lines = get_lines(parts, indent)
                    if len(lines) > 1:
                        lines = []
                        lines.extend(get_lines(opt_parts, indent))
                        lines.extend(get_lines(pos_parts, indent))
                    lines = [prog] + lines

                # join lines into usage
                usage = '\n'.join(lines)

        # prefix with 'usage:'
        return '%s%s\n\n' % (prefix, usage)

    def _format_actions_usage(self, actions, groups):
        # find group indices and identify actions in groups
        group_actions = _set()
        inserts = {}
        for group in groups:
            try:
                start = actions.index(group._group_actions[0])
            except ValueError:
                continue
            else:
                end = start + len(group._group_actions)
                if actions[start:end] == group._group_actions:
                    for action in group._group_actions:
                        group_actions.add(action)
                    if not group.required:
                        inserts[start] = '['
                        inserts[end] = ']'
                    else:
                        inserts[start] = '('
                        inserts[end] = ')'
                    for i in range(start + 1, end):
                        inserts[i] = '|'

        # collect all actions format strings
        parts = []
        for i, action in enumerate(actions):

            # suppressed arguments are marked with None
            # remove | separators for suppressed arguments
            if action.help is SUPPRESS:
                parts.append(None)
                if inserts.get(i) == '|':
                    inserts.pop(i)
                elif inserts.get(i + 1) == '|':
                    inserts.pop(i + 1)

            # produce all arg strings
            elif not action.option_strings:
                part = self._format_args(action, action.dest)

                # if it's in a group, strip the outer []
                if action in group_actions:
                    if part[0] == '[' and part[-1] == ']':
                        part = part[1:-1]

                # add the action string to the list
                parts.append(part)

            # produce the first way to invoke the option in brackets
            else:
                option_string = action.option_strings[0]

                # if the Optional doesn't take a value, format is:
                #    -s or --long
                if action.nargs == 0:
                    part = '%s' % option_string

                # if the Optional takes a value, format is:
                #    -s ARGS or --long ARGS
                else:
                    default = action.dest.upper()
                    args_string = self._format_args(action, default)
                    part = '%s %s' % (option_string, args_string)

                # make it look optional if it's not required or in a group
                if not action.required and action not in group_actions:
                    part = '[%s]' % part

                # add the action string to the list
                parts.append(part)

        # insert things at the necessary indices
        for i in _sorted(inserts, reverse=True):
            parts[i:i] = [inserts[i]]

        # join all the action items with spaces
        text = ' '.join([item for item in parts if item is not None])

        # clean up separators for mutually exclusive groups
        open = r'[\[(]'
        close = r'[\])]'
        text = _re.sub(r'(%s) ' % open, r'\1', text)
        text = _re.sub(r' (%s)' % close, r'\1', text)
        text = _re.sub(r'%s *%s' % (open, close), r'', text)
        text = _re.sub(r'\(([^|]*)\)', r'\1', text)
        text = text.strip()

        # return the text
        return text

    def _format_text(self, text):
        if '%(prog)' in text:
            text = text % dict(prog=self._prog)
        text_width = self._width - self._current_indent
        indent = ' ' * self._current_indent
        return self._fill_text(text, text_width, indent) + '\n\n'

    def _format_action(self, action):
        # determine the required width and the entry label
        help_position = min(self._action_max_length + 2,
                            self._max_help_position)
        help_width = self._width - help_position
        action_width = help_position - self._current_indent - 2
        action_header = self._format_action_invocation(action)

        # ho nelp; start on same line and add a final newline
        if not action.help:
            tup = self._current_indent, '', action_header
            action_header = '%*s%s\n' % tup

        # short action name; start on the same line and pad two spaces
        elif len(action_header) <= action_width:
            tup = self._current_indent, '', action_width, action_header
            action_header = '%*s%-*s  ' % tup
            indent_first = 0

        # long action name; start on the next line
        else:
            tup = self._current_indent, '', action_header
            action_header = '%*s%s\n' % tup
            indent_first = help_position

        # collect the pieces of the action help
        parts = [action_header]

        # if there was help for the action, add lines of help text
        if action.help:
            help_text = self._expand_help(action)
            help_lines = self._split_lines(help_text, help_width)
            parts.append('%*s%s\n' % (indent_first, '', help_lines[0]))
            for line in help_lines[1:]:
                parts.append('%*s%s\n' % (help_position, '', line))

        # or add a newline if the description doesn't end with one
        elif not action_header.endswith('\n'):
            parts.append('\n')

        # if there are any sub-actions, add their help as well
        for subaction in self._iter_indented_subactions(action):
            parts.append(self._format_action(subaction))

        # return a single string
        return self._join_parts(parts)

    def _format_action_invocation(self, action):
        if not action.option_strings:
            metavar, = self._metavar_formatter(action, action.dest)(1)
            return metavar

        else:
            parts = []

            # if the Optional doesn't take a value, format is:
            #    -s, --long
            if action.nargs == 0:
                parts.extend(action.option_strings)

            # if the Optional takes a value, format is:
            #    -s ARGS, --long ARGS
            else:
                default = action.dest.upper()
                args_string = self._format_args(action, default)
                for option_string in action.option_strings:
                    parts.append('%s %s' % (option_string, args_string))

            return ', '.join(parts)

    def _metavar_formatter(self, action, default_metavar):
        if action.metavar is not None:
            result = action.metavar
        elif action.choices is not None:
            choice_strs = [str(choice) for choice in action.choices]
            result = '{%s}' % ','.join(choice_strs)
        else:
            result = default_metavar

        def format(tuple_size):
            if isinstance(result, tuple):
                return result
            else:
                return (result, ) * tuple_size
        return format

    def _format_args(self, action, default_metavar):
        get_metavar = self._metavar_formatter(action, default_metavar)
        if action.nargs is None:
            result = '%s' % get_metavar(1)
        elif action.nargs == OPTIONAL:
            result = '[%s]' % get_metavar(1)
        elif action.nargs == ZERO_OR_MORE:
            result = '[%s [%s ...]]' % get_metavar(2)
        elif action.nargs == ONE_OR_MORE:
            result = '%s [%s ...]' % get_metavar(2)
        elif action.nargs == REMAINDER:
            result = '...'
        elif action.nargs == PARSER:
            result = '%s ...' % get_metavar(1)
        else:
            formats = ['%s' for _ in range(action.nargs)]
            result = ' '.join(formats) % get_metavar(action.nargs)
        return result

    def _expand_help(self, action):
        params = dict(vars(action), prog=self._prog)
        for name in list(params):
            if params[name] is SUPPRESS:
                del params[name]
        if params.get('choices') is not None:
            choices_str = ', '.join([str(c) for c in params['choices']])
            params['choices'] = choices_str
        return self._get_help_string(action) % params

    def _iter_indented_subactions(self, action):
        try:
            get_subactions = action._get_subactions
        except AttributeError:
            pass
        else:
            self._indent()
            for subaction in get_subactions():
                yield subaction
            self._dedent()

    def _split_lines(self, text, width):
        text = self._whitespace_matcher.sub(' ', text).strip()
        return _textwrap.wrap(text, width)

    def _fill_text(self, text, width, indent):
        text = self._whitespace_matcher.sub(' ', text).strip()
        return _textwrap.fill(text, width, initial_indent=indent,
                                           subsequent_indent=indent)

    def _get_help_string(self, action):
        return action.help


class RawDescriptionHelpFormatter(HelpFormatter):
    """Help message formatter which retains any formatting in descriptions.

    Only the name of this class is considered a public API. All the methods
    provided by the class are considered an implementation detail.
    """

    def _fill_text(self, text, width, indent):
        return ''.join([indent + line for line in text.splitlines(True)])


class RawTextHelpFormatter(RawDescriptionHelpFormatter):
    """Help message formatter which retains formatting of all help text.

    Only the name of this class is considered a public API. All the methods
    provided by the class are considered an implementation detail.
    """

    def _split_lines(self, text, width):
        return text.splitlines()


class ArgumentDefaultsHelpFormatter(HelpFormatter):
    """Help message formatter which adds default values to argument help.

    Only the name of this class is considered a public API. All the methods
    provided by the class are considered an implementation detail.
    """

    def _get_help_string(self, action):
        help = action.help
        if '%(default)' not in action.help:
            if action.default is not SUPPRESS:
                defaulting_nargs = [OPTIONAL, ZERO_OR_MORE]
                if action.option_strings or action.nargs in defaulting_nargs:
                    help += ' (default: %(default)s)'
        return help


# =====================
# Options and Arguments
# =====================

def _get_action_name(argument):
    if argument is None:
        return None
    elif argument.option_strings:
        return  '/'.join(argument.option_strings)
    elif argument.metavar not in (None, SUPPRESS):
        return argument.metavar
    elif argument.dest not in (None, SUPPRESS):
        return argument.dest
    else:
        return None


class ArgumentError(Exception):
    """An error from creating or using an argument (optional or positional).

    The string value of this exception is the message, augmented with
    information about the argument that caused it.
    """

    def __init__(self, argument, message):
        self.argument_name = _get_action_name(argument)
        self.message = message

    def __str__(self):
        if self.argument_name is None:
            format = '%(message)s'
        else:
            format = 'argument %(argument_name)s: %(message)s'
        return format % dict(message=self.message,
                             argument_name=self.argument_name)


class ArgumentTypeError(Exception):
    """An error from trying to convert a command line string to a type."""
    pass


# ==============
# Action classes
# ==============

class Action(_AttributeHolder):
    """Information about how to convert command line strings to Python objects.

    Action objects are used by an ArgumentParser to represent the information
    needed to parse a single argument from one or more strings from the
    command line. The keyword arguments to the Action constructor are also
    all attributes of Action instances.

    Keyword Arguments:

        - option_strings -- A list of command-line option strings which
            should be associated with this action.

        - dest -- The name of the attribute to hold the created object(s)

        - nargs -- The number of command-line arguments that should be
            consumed. By default, one argument will be consumed and a single
            value will be produced.  Other values include:
                - N (an integer) consumes N arguments (and produces a list)
                - '?' consumes zero or one arguments
                - '*' consumes zero or more arguments (and produces a list)
                - '+' consumes one or more arguments (and produces a list)
            Note that the difference between the default and nargs=1 is that
            with the default, a single value will be produced, while with
            nargs=1, a list containing a single value will be produced.

        - const -- The value to be produced if the option is specified and the
            option uses an action that takes no values.

        - default -- The value to be produced if the option is not specified.

        - type -- The type which the command-line arguments should be converted
            to, should be one of 'string', 'int', 'float', 'complex' or a
            callable object that accepts a single string argument. If None,
            'string' is assumed.

        - choices -- A container of values that should be allowed. If not None,
            after a command-line argument has been converted to the appropriate
            type, an exception will be raised if it is not a member of this
            collection.

        - required -- True if the action must always be specified at the
            command line. This is only meaningful for optional command-line
            arguments.

        - help -- The help string describing the argument.

        - metavar -- The name to be used for the option's argument with the
            help string. If None, the 'dest' value will be used as the name.
    """

    def __init__(self,
                 option_strings,
                 dest,
                 nargs=None,
                 const=None,
                 default=None,
                 type=None,
                 choices=None,
                 required=False,
                 help=None,
                 metavar=None):
        self.option_strings = option_strings
        self.dest = dest
        self.nargs = nargs
        self.const = const
        self.default = default
        self.type = type
        self.choices = choices
        self.required = required
        self.help = help
        self.metavar = metavar

    def _get_kwargs(self):
        names = [
            'option_strings',
            'dest',
            'nargs',
            'const',
            'default',
            'type',
            'choices',
            'help',
            'metavar',
        ]
        return [(name, getattr(self, name)) for name in names]

    def __call__(self, parser, namespace, values, option_string=None):
        raise NotImplementedError(_('.__call__() not defined'))


class _StoreAction(Action):

    def __init__(self,
                 option_strings,
                 dest,
                 nargs=None,
                 const=None,
                 default=None,
                 type=None,
                 choices=None,
                 required=False,
                 help=None,
                 metavar=None):
        if nargs == 0:
            raise ValueError('nargs for store actions must be > 0; if you '
                             'have nothing to store, actions such as store '
                             'true or store const may be more appropriate')
        if const is not None and nargs != OPTIONAL:
            raise ValueError('nargs must be %r to supply const' % OPTIONAL)
        super(_StoreAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            nargs=nargs,
            const=const,
            default=default,
            type=type,
            choices=choices,
            required=required,
            help=help,
            metavar=metavar)

    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest, values)


class _StoreConstAction(Action):

    def __init__(self,
                 option_strings,
                 dest,
                 const,
                 default=None,
                 required=False,
                 help=None,
                 metavar=None):
        super(_StoreConstAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            nargs=0,
            const=const,
            default=default,
            required=required,
            help=help)

    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest, self.const)


class _StoreTrueAction(_StoreConstAction):

    def __init__(self,
                 option_strings,
                 dest,
                 default=False,
                 required=False,
                 help=None):
        super(_StoreTrueAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            const=True,
            default=default,
            required=required,
            help=help)


class _StoreFalseAction(_StoreConstAction):

    def __init__(self,
                 option_strings,
                 dest,
                 default=True,
                 required=False,
                 help=None):
        super(_StoreFalseAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            const=False,
            default=default,
            required=required,
            help=help)


class _AppendAction(Action):

    def __init__(self,
                 option_strings,
                 dest,
                 nargs=None,
                 const=None,
                 default=None,
                 type=None,
                 choices=None,
                 required=False,
                 help=None,
                 metavar=None):
        if nargs == 0:
            raise ValueError('nargs for append actions must be > 0; if arg '
                             'strings are not supplying the value to append, '
                             'the append const action may be more appropriate')
        if const is not None and nargs != OPTIONAL:
            raise ValueError('nargs must be %r to supply const' % OPTIONAL)
        super(_AppendAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            nargs=nargs,
            const=const,
            default=default,
            type=type,
            choices=choices,
            required=required,
            help=help,
            metavar=metavar)

    def __call__(self, parser, namespace, values, option_string=None):
        items = _copy.copy(_ensure_value(namespace, self.dest, []))
        items.append(values)
        setattr(namespace, self.dest, items)


class _AppendConstAction(Action):

    def __init__(self,
                 option_strings,
                 dest,
                 const,
                 default=None,
                 required=False,
                 help=None,
                 metavar=None):
        super(_AppendConstAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            nargs=0,
            const=const,
            default=default,
            required=required,
            help=help,
            metavar=metavar)

    def __call__(self, parser, namespace, values, option_string=None):
        items = _copy.copy(_ensure_value(namespace, self.dest, []))
        items.append(self.const)
        setattr(namespace, self.dest, items)


class _CountAction(Action):

    def __init__(self,
                 option_strings,
                 dest,
                 default=None,
                 required=False,
                 help=None):
        super(_CountAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            nargs=0,
            default=default,
            required=required,
            help=help)

    def __call__(self, parser, namespace, values, option_string=None):