Added argparse with BSD license.

Taken from:
 http://argparse.googlecode.com/svn/branches/r101-bsd/

This release was made by Steven Bethard, author of argparse, explicitly for
the purpose of providing IPython with a BSD-licensed argparse. Many thanks
to Steven!

IPython/external/argparse.py

@@ -1,2216 +1,2278 b''
 # -*- coding: utf-8 -*-
 
 # Copyright © 2006-2009 Steven J. Bethard <[e-mail]>.
 #
-# 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
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
 #
-#     http://www.apache.org/licenses/LICENSE-2.0
+#  * Redistributions of source code must retain the above copyright notice, this
+#    list of conditions and the following disclaimer.
+#  * Redistributions in binary form must reproduce the above copyright notice,
+#    this list of conditions and the following disclaimer in the documentation
+#    and/or other materials provided with the distribution.
 #
-# 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.
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 """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__ = '1.0'
+__version__ = '1.0.1'
 __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
 
+# 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 = '==PARSER=='
 
 # =============================
 # 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() % dict(prog=self._prog)
+        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
-        if usage is None and not actions:
-            usage = '%(prog)s'
+        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:
-            usage = '%(prog)s' % dict(prog=self._prog)
+            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)
 
-            # determine width of "usage: PROG" and width of text
-            prefix_width = len(prefix) + len(usage) + 1
-            prefix_indent = self._current_indent + prefix_width
-            text_width = self._width - self._current_indent
-
-            # put them on one line if they're short enough
+            # build full usage string
             format = self._format_actions_usage
             action_usage = format(optionals + positionals, groups)
-            if prefix_width + len(action_usage) + 1 < text_width:
-                usage = '%s %s' % (usage, action_usage)
+            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 they're long, wrap optionals and positionals individually
+                # if prog is long, put it on its own line
             else:
-                optional_usage = format(optionals, groups)
-                positional_usage = format(positionals, groups)
-                indent = ' ' * prefix_indent
-
-                # usage is made of PROG, optionals and positionals
-                parts = [usage, ' ']
-
-                # options always get added right after PROG
-                if optional_usage:
-                    parts.append(_textwrap.fill(
-                        optional_usage, text_width,
-                        initial_indent=indent,
-                        subsequent_indent=indent).lstrip())
-
-                # if there were options, put arguments on the next line
-                # otherwise, start them right after PROG
-                if positional_usage:
-                    part = _textwrap.fill(
-                        positional_usage, text_width,
-                        initial_indent=indent,
-                        subsequent_indent=indent).lstrip()
-                    if optional_usage:
-                        part = '\n' + indent + part
-                    parts.append(part)
-                usage = ''.join(parts)
+                    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):
         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 is 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)
 
 # ==============
 # 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 must be > 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 must be > 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):
         new_count = _ensure_value(namespace, self.dest, 0) + 1
         setattr(namespace, self.dest, new_count)
 
 
 class _HelpAction(Action):
 
     def __init__(self,
                  option_strings,
                  dest=SUPPRESS,
                  default=SUPPRESS,
                  help=None):
         super(_HelpAction, self).__init__(
             option_strings=option_strings,
             dest=dest,
             default=default,
             nargs=0,
             help=help)
 
     def __call__(self, parser, namespace, values, option_string=None):
         parser.print_help()
         parser.exit()
 
 
 class _VersionAction(Action):
 
     def __init__(self,
                  option_strings,
                  dest=SUPPRESS,
                  default=SUPPRESS,
                  help=None):
         super(_VersionAction, self).__init__(
             option_strings=option_strings,
             dest=dest,
             default=default,
             nargs=0,
             help=help)
 
     def __call__(self, parser, namespace, values, option_string=None):
         parser.print_version()
         parser.exit()
 
 
 class _SubParsersAction(Action):
 
     class _ChoicesPseudoAction(Action):
 
         def __init__(self, name, help):
             sup = super(_SubParsersAction._ChoicesPseudoAction, self)
             sup.__init__(option_strings=[], dest=name, help=help)
 
     def __init__(self,
                  option_strings,
                  prog,
                  parser_class,
                  dest=SUPPRESS,
                  help=None,
                  metavar=None):
 
         self._prog_prefix = prog
         self._parser_class = parser_class
         self._name_parser_map = {}
         self._choices_actions = []
 
         super(_SubParsersAction, self).__init__(
             option_strings=option_strings,
             dest=dest,
             nargs=PARSER,
             choices=self._name_parser_map,
             help=help,
             metavar=metavar)
 
     def add_parser(self, name, **kwargs):
         # set prog from the existing prefix
         if kwargs.get('prog') is None:
             kwargs['prog'] = '%s %s' % (self._prog_prefix, name)
 
         # create a pseudo-action to hold the choice help
         if 'help' in kwargs:
             help = kwargs.pop('help')
             choice_action = self._ChoicesPseudoAction(name, help)
             self._choices_actions.append(choice_action)
 
         # create the parser and add it to the map
         parser = self._parser_class(**kwargs)
         self._name_parser_map[name] = parser
         return parser
 
     def _get_subactions(self):
         return self._choices_actions
 
     def __call__(self, parser, namespace, values, option_string=None):
         parser_name = values[0]
         arg_strings = values[1:]
 
         # set the parser name if requested
         if self.dest is not SUPPRESS:
             setattr(namespace, self.dest, parser_name)
 
         # select the parser
         try:
             parser = self._name_parser_map[parser_name]
         except KeyError:
             tup = parser_name, ', '.join(self._name_parser_map)
             msg = _('unknown parser %r (choices: %s)' % tup)
             raise ArgumentError(self, msg)
 
         # parse all the remaining options into the namespace
         parser.parse_args(arg_strings, namespace)
 
 
 # ==============
 # Type classes
 # ==============
 
 class FileType(object):
     """Factory for creating file object types
 
     Instances of FileType are typically passed as type= arguments to the
     ArgumentParser add_argument() method.
 
     Keyword Arguments:
         - mode -- A string indicating how the file is to be opened. Accepts the
             same values as the builtin open() function.
         - bufsize -- The file's desired buffer size. Accepts the same values as
             the builtin open() function.
     """
 
     def __init__(self, mode='r', bufsize=None):
         self._mode = mode
         self._bufsize = bufsize
 
     def __call__(self, string):
         # the special argument "-" means sys.std{in,out}
         if string == '-':
             if 'r' in self._mode:
                 return _sys.stdin
             elif 'w' in self._mode:
                 return _sys.stdout
             else:
                 msg = _('argument "-" with mode %r' % self._mode)
                 raise ValueError(msg)
 
         # all other arguments are used as file names
         if self._bufsize:
             return open(string, self._mode, self._bufsize)
         else:
             return open(string, self._mode)
 
     def __repr__(self):
         args = [self._mode, self._bufsize]
         args_str = ', '.join([repr(arg) for arg in args if arg is not None])
         return '%s(%s)' % (type(self).__name__, args_str)
 
 # ===========================
 # Optional and Positional Parsing
 # ===========================
 
 class Namespace(_AttributeHolder):
     """Simple object for storing attributes.
 
     Implements equality by attribute names and values, and provides a simple
     string representation.
     """
 
     def __init__(self, **kwargs):
         for name in kwargs:
             setattr(self, name, kwargs[name])
 
     def __eq__(self, other):
         return vars(self) == vars(other)
 
     def __ne__(self, other):
         return not (self == other)
 
 
 class _ActionsContainer(object):
 
     def __init__(self,
                  description,
                  prefix_chars,
                  argument_default,
                  conflict_handler):
         super(_ActionsContainer, self).__init__()
 
         self.description = description
         self.argument_default = argument_default
         self.prefix_chars = prefix_chars
         self.conflict_handler = conflict_handler
 
         # set up registries
         self._registries = {}
 
         # register actions
         self.register('action', None, _StoreAction)
         self.register('action', 'store', _StoreAction)
         self.register('action', 'store_const', _StoreConstAction)
         self.register('action', 'store_true', _StoreTrueAction)
         self.register('action', 'store_false', _StoreFalseAction)
         self.register('action', 'append', _AppendAction)
         self.register('action', 'append_const', _AppendConstAction)
         self.register('action', 'count', _CountAction)
         self.register('action', 'help', _HelpAction)
         self.register('action', 'version', _VersionAction)
         self.register('action', 'parsers', _SubParsersAction)
 
         # raise an exception if the conflict handler is invalid
         self._get_handler()
 
         # action storage
         self._actions = []
         self._option_string_actions = {}
 
         # groups
         self._action_groups = []
         self._mutually_exclusive_groups = []
 
         # defaults storage
         self._defaults = {}
 
         # determines whether an "option" looks like a negative number
         self._negative_number_matcher = _re.compile(r'^-\d+|-\d*.\d+$')
 
         # whether or not there are any optionals that look like negative
         # numbers -- uses a list so it can be shared and edited
         self._has_negative_number_optionals = []
 
     # ====================
     # Registration methods
     # ====================
     def register(self, registry_name, value, object):
         registry = self._registries.setdefault(registry_name, {})
         registry[value] = object
 
     def _registry_get(self, registry_name, value, default=None):
         return self._registries[registry_name].get(value, default)
 
     # ==================================
     # Namespace default settings methods
     # ==================================
     def set_defaults(self, **kwargs):
         self._defaults.update(kwargs)
 
         # if these defaults match any existing arguments, replace
         # the previous default on the object with the new one
         for action in self._actions:
             if action.dest in kwargs:
                 action.default = kwargs[action.dest]
 
     # =======================
     # Adding argument actions
     # =======================
     def add_argument(self, *args, **kwargs):
         """
         add_argument(dest, ..., name=value, ...)
         add_argument(option_string, option_string, ..., name=value, ...)
         """
 
         # if no positional args are supplied or only one is supplied and
         # it doesn't look like an option string, parse a positional
         # argument
         chars = self.prefix_chars
         if not args or len(args) == 1 and args[0][0] not in chars:
             kwargs = self._get_positional_kwargs(*args, **kwargs)
 
         # otherwise, we're adding an optional argument
         else:
             kwargs = self._get_optional_kwargs(*args, **kwargs)
 
         # if no default was supplied, use the parser-level default
         if 'default' not in kwargs:
             dest = kwargs['dest']
             if dest in self._defaults:
                 kwargs['default'] = self._defaults[dest]
             elif self.argument_default is not None:
                 kwargs['default'] = self.argument_default
 
         # create the action object, and add it to the parser
         action_class = self._pop_action_class(kwargs)
         action = action_class(**kwargs)
         return self._add_action(action)
 
     def add_argument_group(self, *args, **kwargs):
         group = _ArgumentGroup(self, *args, **kwargs)
         self._action_groups.append(group)
         return group
 
     def add_mutually_exclusive_group(self, **kwargs):
         group = _MutuallyExclusiveGroup(self, **kwargs)
         self._mutually_exclusive_groups.append(group)
         return group
 
     def _add_action(self, action):
         # resolve any conflicts
         self._check_conflict(action)
 
         # add to actions list
         self._actions.append(action)
         action.container = self
 
         # index the action by any option strings it has
         for option_string in action.option_strings:
             self._option_string_actions[option_string] = action
 
         # set the flag if any option strings look like negative numbers
         for option_string in action.option_strings:
             if self._negative_number_matcher.match(option_string):
                 if not self._has_negative_number_optionals:
                     self._has_negative_number_optionals.append(True)
 
         # return the created action
         return action
 
     def _remove_action(self, action):
         self._actions.remove(action)
 
     def _add_container_actions(self, container):
         # collect groups by titles
         title_group_map = {}
         for group in self._action_groups:
             if group.title in title_group_map:
                 msg = _('cannot merge actions - two groups are named %r')
                 raise ValueError(msg % (group.title))
             title_group_map[group.title] = group
 
         # map each action to its group
         group_map = {}
         for group in container._action_groups:
 
             # if a group with the title exists, use that, otherwise
             # create a new group matching the container's group
             if group.title not in title_group_map:
                 title_group_map[group.title] = self.add_argument_group(
                     title=group.title,
                     description=group.description,
                     conflict_handler=group.conflict_handler)
 
             # map the actions to their new group
             for action in group._group_actions:
                 group_map[action] = title_group_map[group.title]
 
+        # add container's mutually exclusive groups
+        # NOTE: if add_mutually_exclusive_group ever gains title= and
+        # description= then this code will need to be expanded as above
+        for group in container._mutually_exclusive_groups:
+            mutex_group = self.add_mutually_exclusive_group(
+                required=group.required)
+
+            # map the actions to their new mutex group
+            for action in group._group_actions:
+                group_map[action] = mutex_group
+
         # add all actions to this container or their group
         for action in container._actions:
             group_map.get(action, self)._add_action(action)
 
     def _get_positional_kwargs(self, dest, **kwargs):
         # make sure required is not specified
         if 'required' in kwargs:
             msg = _("'required' is an invalid argument for positionals")
             raise TypeError(msg)
 
         # mark positional arguments as required if at least one is
         # always required
         if kwargs.get('nargs') not in [OPTIONAL, ZERO_OR_MORE]:
             kwargs['required'] = True
         if kwargs.get('nargs') == ZERO_OR_MORE and 'default' not in kwargs:
             kwargs['required'] = True
 
         # return the keyword arguments with no option strings
         return dict(kwargs, dest=dest, option_strings=[])
 
     def _get_optional_kwargs(self, *args, **kwargs):
         # determine short and long option strings
         option_strings = []
         long_option_strings = []
         for option_string in args:
             # error on one-or-fewer-character option strings
             if len(option_string) < 2:
                 msg = _('invalid option string %r: '
                         'must be at least two characters long')
                 raise ValueError(msg % option_string)
 
             # error on strings that don't start with an appropriate prefix
             if not option_string[0] in self.prefix_chars:
                 msg = _('invalid option string %r: '
                         'must start with a character %r')
                 tup = option_string, self.prefix_chars
                 raise ValueError(msg % tup)
 
             # error on strings that are all prefix characters
             if not (_set(option_string) - _set(self.prefix_chars)):
                 msg = _('invalid option string %r: '
                         'must contain characters other than %r')
                 tup = option_string, self.prefix_chars
                 raise ValueError(msg % tup)
 
             # strings starting with two prefix characters are long options
             option_strings.append(option_string)
             if option_string[0] in self.prefix_chars:
                 if option_string[1] in self.prefix_chars:
                     long_option_strings.append(option_string)
 
         # infer destination, '--foo-bar' -> 'foo_bar' and '-x' -> 'x'
         dest = kwargs.pop('dest', None)
         if dest is None:
             if long_option_strings:
                 dest_option_string = long_option_strings[0]
             else:
                 dest_option_string = option_strings[0]
             dest = dest_option_string.lstrip(self.prefix_chars)
             dest = dest.replace('-', '_')
 
         # return the updated keyword arguments
         return dict(kwargs, dest=dest, option_strings=option_strings)
 
     def _pop_action_class(self, kwargs, default=None):
         action = kwargs.pop('action', default)
         return self._registry_get('action', action, action)
 
     def _get_handler(self):
         # determine function from conflict handler string
         handler_func_name = '_handle_conflict_%s' % self.conflict_handler
         try:
             return getattr(self, handler_func_name)
         except AttributeError:
             msg = _('invalid conflict_resolution value: %r')
             raise ValueError(msg % self.conflict_handler)
 
     def _check_conflict(self, action):
 
         # find all options that conflict with this option
         confl_optionals = []
         for option_string in action.option_strings:
             if option_string in self._option_string_actions:
                 confl_optional = self._option_string_actions[option_string]
                 confl_optionals.append((option_string, confl_optional))
 
         # resolve any conflicts
         if confl_optionals:
             conflict_handler = self._get_handler()
             conflict_handler(action, confl_optionals)
 
     def _handle_conflict_error(self, action, conflicting_actions):
         message = _('conflicting option string(s): %s')
         conflict_string = ', '.join([option_string
                                      for option_string, action
                                      in conflicting_actions])
         raise ArgumentError(action, message % conflict_string)
 
     def _handle_conflict_resolve(self, action, conflicting_actions):
 
         # remove all conflicting options
         for option_string, action in conflicting_actions:
 
             # remove the conflicting option
             action.option_strings.remove(option_string)
             self._option_string_actions.pop(option_string, None)
 
             # if the option now has no option string, remove it from the
             # container holding it
             if not action.option_strings:
                 action.container._remove_action(action)
 
 
 class _ArgumentGroup(_ActionsContainer):
 
     def __init__(self, container, title=None, description=None, **kwargs):
         # add any missing keyword arguments by checking the container
         update = kwargs.setdefault
         update('conflict_handler', container.conflict_handler)
         update('prefix_chars', container.prefix_chars)
         update('argument_default', container.argument_default)
         super_init = super(_ArgumentGroup, self).__init__
         super_init(description=description, **kwargs)
 
         # group attributes
         self.title = title
         self._group_actions = []
 
         # share most attributes with the container
         self._registries = container._registries
         self._actions = container._actions
         self._option_string_actions = container._option_string_actions
         self._defaults = container._defaults
         self._has_negative_number_optionals = \
             container._has_negative_number_optionals
 
     def _add_action(self, action):
         action = super(_ArgumentGroup, self)._add_action(action)
         self._group_actions.append(action)
         return action
 
     def _remove_action(self, action):
         super(_ArgumentGroup, self)._remove_action(action)
         self._group_actions.remove(action)
 
 
 class _MutuallyExclusiveGroup(_ArgumentGroup):
 
     def __init__(self, container, required=False):
         super(_MutuallyExclusiveGroup, self).__init__(container)
         self.required = required
         self._container = container
 
     def _add_action(self, action):
         if action.required:
             msg = _('mutually exclusive arguments must be optional')
             raise ValueError(msg)
         action = self._container._add_action(action)
         self._group_actions.append(action)
         return action
 
     def _remove_action(self, action):
         self._container._remove_action(action)
         self._group_actions.remove(action)
 
 
 class ArgumentParser(_AttributeHolder, _ActionsContainer):
     """Object for parsing command line strings into Python objects.
 
     Keyword Arguments:
         - prog -- The name of the program (default: sys.argv[0])
         - usage -- A usage message (default: auto-generated from arguments)
         - description -- A description of what the program does
         - epilog -- Text following the argument descriptions
         - version -- Add a -v/--version option with the given version string
         - parents -- Parsers whose arguments should be copied into this one
         - formatter_class -- HelpFormatter class for printing help messages
         - prefix_chars -- Characters that prefix optional arguments
         - fromfile_prefix_chars -- Characters that prefix files containing
             additional arguments
         - argument_default -- The default value for all arguments
         - conflict_handler -- String indicating how to handle conflicts
         - add_help -- Add a -h/-help option
     """
 
     def __init__(self,
                  prog=None,
                  usage=None,
                  description=None,
                  epilog=None,
                  version=None,
                  parents=[],
                  formatter_class=HelpFormatter,
                  prefix_chars='-',
                  fromfile_prefix_chars=None,
                  argument_default=None,
                  conflict_handler='error',
                  add_help=True):
 
         superinit = super(ArgumentParser, self).__init__
         superinit(description=description,
                   prefix_chars=prefix_chars,
                   argument_default=argument_default,
                   conflict_handler=conflict_handler)
 
         # default setting for prog
         if prog is None:
             prog = _os.path.basename(_sys.argv[0])
 
         self.prog = prog
         self.usage = usage
         self.epilog = epilog
         self.version = version
         self.formatter_class = formatter_class
         self.fromfile_prefix_chars = fromfile_prefix_chars
         self.add_help = add_help
 
         add_group = self.add_argument_group
         self._positionals = add_group(_('positional arguments'))
         self._optionals = add_group(_('optional arguments'))
         self._subparsers = None
 
         # register types
         def identity(string):
             return string
         self.register('type', None, identity)
 
         # add help and version arguments if necessary
         # (using explicit default to override global argument_default)
         if self.add_help:
             self.add_argument(
                 '-h', '--help', action='help', default=SUPPRESS,
                 help=_('show this help message and exit'))
         if self.version:
             self.add_argument(
                 '-v', '--version', action='version', default=SUPPRESS,
                 help=_("show program's version number and exit"))
 
         # add parent arguments and defaults
         for parent in parents:
             self._add_container_actions(parent)
             try:
                 defaults = parent._defaults
             except AttributeError:
                 pass
             else:
                 self._defaults.update(defaults)
 
     # =======================
     # Pretty __repr__ methods
     # =======================
     def _get_kwargs(self):
         names = [
             'prog',
             'usage',
             'description',
             'version',
             'formatter_class',
             'conflict_handler',
             'add_help',
         ]
         return [(name, getattr(self, name)) for name in names]
 
     # ==================================
     # Optional/Positional adding methods
     # ==================================
     def add_subparsers(self, **kwargs):
         if self._subparsers is not None:
             self.error(_('cannot have multiple subparser arguments'))
 
         # add the parser class to the arguments if it's not present
         kwargs.setdefault('parser_class', type(self))
 
         if 'title' in kwargs or 'description' in kwargs:
             title = _(kwargs.pop('title', 'subcommands'))
             description = _(kwargs.pop('description', None))
             self._subparsers = self.add_argument_group(title, description)
         else:
             self._subparsers = self._positionals
 
         # prog defaults to the usage message of this parser, skipping
         # optional arguments and with no "usage:" prefix
         if kwargs.get('prog') is None:
             formatter = self._get_formatter()
             positionals = self._get_positional_actions()
             groups = self._mutually_exclusive_groups
             formatter.add_usage(self.usage, positionals, groups, '')
             kwargs['prog'] = formatter.format_help().strip()
 
         # create the parsers action and add it to the positionals list
         parsers_class = self._pop_action_class(kwargs, 'parsers')
         action = parsers_class(option_strings=[], **kwargs)
         self._subparsers._add_action(action)
 
         # return the created parsers action
         return action
 
     def _add_action(self, action):
         if action.option_strings:
             self._optionals._add_action(action)
         else:
             self._positionals._add_action(action)
         return action
 
     def _get_optional_actions(self):
         return [action
                 for action in self._actions
                 if action.option_strings]
 
     def _get_positional_actions(self):
         return [action
                 for action in self._actions
                 if not action.option_strings]
 
     # =====================================
     # Command line argument parsing methods
     # =====================================
     def parse_args(self, args=None, namespace=None):
         args, argv = self.parse_known_args(args, namespace)
         if argv:
             msg = _('unrecognized arguments: %s')
             self.error(msg % ' '.join(argv))
         return args
 
     def parse_known_args(self, args=None, namespace=None):
         # args default to the system args
         if args is None:
             args = _sys.argv[1:]
 
         # default Namespace built from parser defaults
         if namespace is None:
             namespace = Namespace()
 
         # add any action defaults that aren't present
         for action in self._actions:
             if action.dest is not SUPPRESS:
                 if not hasattr(namespace, action.dest):
                     if action.default is not SUPPRESS:
                         default = action.default
                         if isinstance(action.default, _basestring):
                             default = self._get_value(action, default)
                         setattr(namespace, action.dest, default)
 
         # add any parser defaults that aren't present
         for dest in self._defaults:
             if not hasattr(namespace, dest):
                 setattr(namespace, dest, self._defaults[dest])
 
         # parse the arguments and exit if there are any errors
         try:
             return self._parse_known_args(args, namespace)
         except ArgumentError:
             err = _sys.exc_info()[1]
             self.error(str(err))
 
     def _parse_known_args(self, arg_strings, namespace):
         # replace arg strings that are file references
         if self.fromfile_prefix_chars is not None:
             arg_strings = self._read_args_from_files(arg_strings)
 
         # map all mutually exclusive arguments to the other arguments
         # they can't occur with
         action_conflicts = {}
         for mutex_group in self._mutually_exclusive_groups:
             group_actions = mutex_group._group_actions
             for i, mutex_action in enumerate(mutex_group._group_actions):
                 conflicts = action_conflicts.setdefault(mutex_action, [])
                 conflicts.extend(group_actions[:i])
                 conflicts.extend(group_actions[i + 1:])
 
         # find all option indices, and determine the arg_string_pattern
         # which has an 'O' if there is an option at an index,
         # an 'A' if there is an argument, or a '-' if there is a '--'
         option_string_indices = {}
         arg_string_pattern_parts = []
         arg_strings_iter = iter(arg_strings)
         for i, arg_string in enumerate(arg_strings_iter):
 
             # all args after -- are non-options
             if arg_string == '--':
                 arg_string_pattern_parts.append('-')
                 for arg_string in arg_strings_iter:
                     arg_string_pattern_parts.append('A')
 
             # otherwise, add the arg to the arg strings
             # and note the index if it was an option
             else:
                 option_tuple = self._parse_optional(arg_string)
                 if option_tuple is None:
                     pattern = 'A'
                 else:
                     option_string_indices[i] = option_tuple
                     pattern = 'O'
                 arg_string_pattern_parts.append(pattern)
 
         # join the pieces together to form the pattern
         arg_strings_pattern = ''.join(arg_string_pattern_parts)
 
         # converts arg strings to the appropriate and then takes the action
         seen_actions = _set()
         seen_non_default_actions = _set()
 
         def take_action(action, argument_strings, option_string=None):
             seen_actions.add(action)
             argument_values = self._get_values(action, argument_strings)
 
             # error if this argument is not allowed with other previously
             # seen arguments, assuming that actions that use the default
             # value don't really count as "present"
             if argument_values is not action.default:
                 seen_non_default_actions.add(action)
                 for conflict_action in action_conflicts.get(action, []):
                     if conflict_action in seen_non_default_actions:
                         msg = _('not allowed with argument %s')
                         action_name = _get_action_name(conflict_action)
                         raise ArgumentError(action, msg % action_name)
 
             # take the action if we didn't receive a SUPPRESS value
             # (e.g. from a default)
             if argument_values is not SUPPRESS:
                 action(self, namespace, argument_values, option_string)
 
         # function to convert arg_strings into an optional action
         def consume_optional(start_index):
 
             # get the optional identified at this index
             option_tuple = option_string_indices[start_index]
             action, option_string, explicit_arg = option_tuple
 
             # identify additional optionals in the same arg string
             # (e.g. -xyz is the same as -x -y -z if no args are required)
             match_argument = self._match_argument
             action_tuples = []
             while True:
 
                 # if we found no optional action, skip it
                 if action is None:
                     extras.append(arg_strings[start_index])
                     return start_index + 1
 
                 # if there is an explicit argument, try to match the
                 # optional's string arguments to only this
                 if explicit_arg is not None:
                     arg_count = match_argument(action, 'A')
 
                     # if the action is a single-dash option and takes no
                     # arguments, try to parse more single-dash options out
                     # of the tail of the option string
                     chars = self.prefix_chars
                     if arg_count == 0 and option_string[1] not in chars:
                         action_tuples.append((action, [], option_string))
                         for char in self.prefix_chars:
                             option_string = char + explicit_arg[0]
                             explicit_arg = explicit_arg[1:] or None
                             optionals_map = self._option_string_actions
                             if option_string in optionals_map:
                                 action = optionals_map[option_string]
                                 break
                         else:
                             msg = _('ignored explicit argument %r')
                             raise ArgumentError(action, msg % explicit_arg)
 
                     # if the action expect exactly one argument, we've
                     # successfully matched the option; exit the loop
                     elif arg_count == 1:
                         stop = start_index + 1
                         args = [explicit_arg]
                         action_tuples.append((action, args, option_string))
                         break
 
                     # error if a double-dash option did not use the
                     # explicit argument
                     else:
                         msg = _('ignored explicit argument %r')
                         raise ArgumentError(action, msg % explicit_arg)
 
                 # if there is no explicit argument, try to match the
                 # optional's string arguments with the following strings
                 # if successful, exit the loop
                 else:
                     start = start_index + 1
                     selected_patterns = arg_strings_pattern[start:]
                     arg_count = match_argument(action, selected_patterns)
                     stop = start + arg_count
                     args = arg_strings[start:stop]
                     action_tuples.append((action, args, option_string))
                     break
 
             # add the Optional to the list and return the index at which
             # the Optional's string args stopped
             assert action_tuples
             for action, args, option_string in action_tuples:
                 take_action(action, args, option_string)
             return stop
 
         # the list of Positionals left to be parsed; this is modified
         # by consume_positionals()
         positionals = self._get_positional_actions()
 
         # function to convert arg_strings into positional actions
         def consume_positionals(start_index):
             # match as many Positionals as possible
             match_partial = self._match_arguments_partial
             selected_pattern = arg_strings_pattern[start_index:]
             arg_counts = match_partial(positionals, selected_pattern)
 
             # slice off the appropriate arg strings for each Positional
             # and add the Positional and its args to the list
             for action, arg_count in zip(positionals, arg_counts):
                 args = arg_strings[start_index: start_index + arg_count]
                 start_index += arg_count
                 take_action(action, args)
 
             # slice off the Positionals that we just parsed and return the
             # index at which the Positionals' string args stopped
             positionals[:] = positionals[len(arg_counts):]
             return start_index
 
         # consume Positionals and Optionals alternately, until we have
         # passed the last option string
         extras = []
         start_index = 0
         if option_string_indices:
             max_option_string_index = max(option_string_indices)
         else:
             max_option_string_index = -1
         while start_index <= max_option_string_index:
 
             # consume any Positionals preceding the next option
             next_option_string_index = min([
                 index
                 for index in option_string_indices
                 if index >= start_index])
             if start_index != next_option_string_index:
                 positionals_end_index = consume_positionals(start_index)
 
                 # only try to parse the next optional if we didn't consume
                 # the option string during the positionals parsing
                 if positionals_end_index > start_index:
                     start_index = positionals_end_index
                     continue
                 else:
                     start_index = positionals_end_index
 
             # if we consumed all the positionals we could and we're not
             # at the index of an option string, there were extra arguments
             if start_index not in option_string_indices:
                 strings = arg_strings[start_index:next_option_string_index]
                 extras.extend(strings)
                 start_index = next_option_string_index
 
             # consume the next optional and any arguments for it
             start_index = consume_optional(start_index)
 
         # consume any positionals following the last Optional
         stop_index = consume_positionals(start_index)
 
         # if we didn't consume all the argument strings, there were extras
         extras.extend(arg_strings[stop_index:])
 
         # if we didn't use all the Positional objects, there were too few
         # arg strings supplied.
         if positionals:
             self.error(_('too few arguments'))
 
         # make sure all required actions were present
         for action in self._actions:
             if action.required:
                 if action not in seen_actions:
                     name = _get_action_name(action)
                     self.error(_('argument %s is required') % name)
 
         # make sure all required groups had one option present
         for group in self._mutually_exclusive_groups:
             if group.required:
                 for action in group._group_actions:
                     if action in seen_non_default_actions:
                         break
 
                 # if no actions were used, report the error
                 else:
                     names = [_get_action_name(action)
                              for action in group._group_actions
                              if action.help is not SUPPRESS]
                     msg = _('one of the arguments %s is required')
                     self.error(msg % ' '.join(names))
 
         # return the updated namespace and the extra arguments
         return namespace, extras
 
     def _read_args_from_files(self, arg_strings):
         # expand arguments referencing files
         new_arg_strings = []
         for arg_string in arg_strings:
 
             # for regular arguments, just add them back into the list
             if arg_string[0] not in self.fromfile_prefix_chars:
                 new_arg_strings.append(arg_string)
 
             # replace arguments referencing files with the file content
             else:
                 try:
                     args_file = open(arg_string[1:])
                     try:
                         arg_strings = args_file.read().splitlines()
                         arg_strings = self._read_args_from_files(arg_strings)
                         new_arg_strings.extend(arg_strings)
                     finally:
                         args_file.close()
                 except IOError:
                     err = _sys.exc_info()[1]
                     self.error(str(err))
 
         # return the modified argument list
         return new_arg_strings
 
     def _match_argument(self, action, arg_strings_pattern):
         # match the pattern for this action to the arg strings
         nargs_pattern = self._get_nargs_pattern(action)
         match = _re.match(nargs_pattern, arg_strings_pattern)
 
         # raise an exception if we weren't able to find a match
         if match is None:
             nargs_errors = {
                 None: _('expected one argument'),
                 OPTIONAL: _('expected at most one argument'),
                 ONE_OR_MORE: _('expected at least one argument'),
             }
             default = _('expected %s argument(s)') % action.nargs
             msg = nargs_errors.get(action.nargs, default)
             raise ArgumentError(action, msg)
 
         # return the number of arguments matched
         return len(match.group(1))
 
     def _match_arguments_partial(self, actions, arg_strings_pattern):
         # progressively shorten the actions list by slicing off the
         # final actions until we find a match
         result = []
         for i in range(len(actions), 0, -1):
             actions_slice = actions[:i]
             pattern = ''.join([self._get_nargs_pattern(action)
                                for action in actions_slice])
             match = _re.match(pattern, arg_strings_pattern)
             if match is not None:
                 result.extend([len(string) for string in match.groups()])
                 break
 
         # return the list of arg string counts
         return result
 
     def _parse_optional(self, arg_string):
         # if it's an empty string, it was meant to be a positional
         if not arg_string:
             return None
 
         # if it doesn't start with a prefix, it was meant to be positional
         if not arg_string[0] in self.prefix_chars:
             return None
 
         # if it's just dashes, it was meant to be positional
         if not arg_string.strip('-'):
             return None
 
         # if the option string is present in the parser, return the action
         if arg_string in self._option_string_actions:
             action = self._option_string_actions[arg_string]
             return action, arg_string, None
 
         # search through all possible prefixes of the option string
         # and all actions in the parser for possible interpretations
         option_tuples = self._get_option_tuples(arg_string)
 
         # if multiple actions match, the option string was ambiguous
         if len(option_tuples) > 1:
             options = ', '.join([option_string
                 for action, option_string, explicit_arg in option_tuples])
             tup = arg_string, options
             self.error(_('ambiguous option: %s could match %s') % tup)
 
         # if exactly one action matched, this segmentation is good,
         # so return the parsed action
         elif len(option_tuples) == 1:
             option_tuple, = option_tuples
             return option_tuple
 
         # if it was not found as an option, but it looks like a negative
         # number, it was meant to be positional
         # unless there are negative-number-like options
         if self._negative_number_matcher.match(arg_string):
             if not self._has_negative_number_optionals:
                 return None
 
         # if it contains a space, it was meant to be a positional
         if ' ' in arg_string:
             return None
 
         # it was meant to be an optional but there is no such option
         # in this parser (though it might be a valid option in a subparser)
         return None, arg_string, None
 
     def _get_option_tuples(self, option_string):
         result = []
 
         # option strings starting with two prefix characters are only
         # split at the '='
         chars = self.prefix_chars
         if option_string[0] in chars and option_string[1] in chars:
             if '=' in option_string:
                 option_prefix, explicit_arg = option_string.split('=', 1)
             else:
                 option_prefix = option_string
                 explicit_arg = None
             for option_string in self._option_string_actions:
                 if option_string.startswith(option_prefix):
                     action = self._option_string_actions[option_string]
                     tup = action, option_string, explicit_arg
                     result.append(tup)
 
         # single character options can be concatenated with their arguments
         # but multiple character options always have to have their argument
         # separate
         elif option_string[0] in chars and option_string[1] not in chars:
             option_prefix = option_string
             explicit_arg = None
             short_option_prefix = option_string[:2]
             short_explicit_arg = option_string[2:]
 
             for option_string in self._option_string_actions:
                 if option_string == short_option_prefix:
                     action = self._option_string_actions[option_string]
                     tup = action, option_string, short_explicit_arg
                     result.append(tup)
                 elif option_string.startswith(option_prefix):
                     action = self._option_string_actions[option_string]
                     tup = action, option_string, explicit_arg
                     result.append(tup)
 
         # shouldn't ever get here
         else:
             self.error(_('unexpected option string: %s') % option_string)
 
         # return the collected option tuples
         return result
 
     def _get_nargs_pattern(self, action):
         # in all examples below, we have to allow for '--' args
         # which are represented as '-' in the pattern
         nargs = action.nargs
 
         # the default (None) is assumed to be a single argument
         if nargs is None:
             nargs_pattern = '(-*A-*)'
 
         # allow zero or one arguments
         elif nargs == OPTIONAL:
             nargs_pattern = '(-*A?-*)'
 
         # allow zero or more arguments
         elif nargs == ZERO_OR_MORE:
             nargs_pattern = '(-*[A-]*)'
 
         # allow one or more arguments
         elif nargs == ONE_OR_MORE:
             nargs_pattern = '(-*A[A-]*)'
 
         # allow one argument followed by any number of options or arguments
         elif nargs is PARSER:
             nargs_pattern = '(-*A[-AO]*)'
 
         # all others should be integers
         else:
             nargs_pattern = '(-*%s-*)' % '-*'.join('A' * nargs)
 
         # if this is an optional action, -- is not allowed
         if action.option_strings:
             nargs_pattern = nargs_pattern.replace('-*', '')
             nargs_pattern = nargs_pattern.replace('-', '')
 
         # return the pattern
         return nargs_pattern
 
     # ========================
     # Value conversion methods
     # ========================
     def _get_values(self, action, arg_strings):
         # for everything but PARSER args, strip out '--'
         if action.nargs is not PARSER:
             arg_strings = [s for s in arg_strings if s != '--']
 
         # optional argument produces a default when not present
         if not arg_strings and action.nargs == OPTIONAL:
             if action.option_strings:
                 value = action.const
             else:
                 value = action.default
             if isinstance(value, _basestring):
                 value = self._get_value(action, value)
                 self._check_value(action, value)
 
         # when nargs='*' on a positional, if there were no command-line
         # args, use the default if it is anything other than None
         elif (not arg_strings and action.nargs == ZERO_OR_MORE and
               not action.option_strings):
             if action.default is not None:
                 value = action.default
             else:
                 value = arg_strings
             self._check_value(action, value)
 
         # single argument or optional argument produces a single value
         elif len(arg_strings) == 1 and action.nargs in [None, OPTIONAL]:
             arg_string, = arg_strings
             value = self._get_value(action, arg_string)
             self._check_value(action, value)
 
         # PARSER arguments convert all values, but check only the first
         elif action.nargs is PARSER:
             value = [self._get_value(action, v) for v in arg_strings]
             self._check_value(action, value[0])
 
         # all other types of nargs produce a list
         else:
             value = [self._get_value(action, v) for v in arg_strings]
             for v in value:
                 self._check_value(action, v)
 
         # return the converted value
         return value
 
     def _get_value(self, action, arg_string):
         type_func = self._registry_get('type', action.type, action.type)
         if not hasattr(type_func, '__call__'):
+            if not hasattr(type_func, '__bases__'): # classic classes
             msg = _('%r is not callable')
             raise ArgumentError(action, msg % type_func)
 
         # convert the value to the appropriate type
         try:
             result = type_func(arg_string)
 
         # TypeErrors or ValueErrors indicate errors
         except (TypeError, ValueError):
             name = getattr(action.type, '__name__', repr(action.type))
             msg = _('invalid %s value: %r')
             raise ArgumentError(action, msg % (name, arg_string))
 
         # return the converted value
         return result
 
     def _check_value(self, action, value):
         # converted value must be one of the choices (if specified)
         if action.choices is not None and value not in action.choices:
             tup = value, ', '.join(map(repr, action.choices))
             msg = _('invalid choice: %r (choose from %s)') % tup
             raise ArgumentError(action, msg)
 
     # =======================
     # Help-formatting methods
     # =======================
     def format_usage(self):
         formatter = self._get_formatter()
         formatter.add_usage(self.usage, self._actions,
                             self._mutually_exclusive_groups)
         return formatter.format_help()
 
     def format_help(self):
         formatter = self._get_formatter()
 
         # usage
         formatter.add_usage(self.usage, self._actions,
                             self._mutually_exclusive_groups)
 
         # description
         formatter.add_text(self.description)
 
         # positionals, optionals and user-defined groups
         for action_group in self._action_groups:
             formatter.start_section(action_group.title)
             formatter.add_text(action_group.description)
             formatter.add_arguments(action_group._group_actions)
             formatter.end_section()
 
         # epilog
         formatter.add_text(self.epilog)
 
         # determine help from format above
         return formatter.format_help()
 
     def format_version(self):
         formatter = self._get_formatter()
         formatter.add_text(self.version)
         return formatter.format_help()
 
     def _get_formatter(self):
         return self.formatter_class(prog=self.prog)
 
     # =====================
     # Help-printing methods
     # =====================
     def print_usage(self, file=None):
         self._print_message(self.format_usage(), file)
 
     def print_help(self, file=None):
         self._print_message(self.format_help(), file)
 
     def print_version(self, file=None):
         self._print_message(self.format_version(), file)
 
     def _print_message(self, message, file=None):
         if message:
             if file is None:
                 file = _sys.stderr
             file.write(message)
 
     # ===============
     # Exiting methods
     # ===============
     def exit(self, status=0, message=None):
         if message:
             _sys.stderr.write(message)
         _sys.exit(status)
 
     def error(self, message):
         """error(message: string)
 
         Prints a usage message incorporating the message to stderr and
         exits.
 
         If you override this in a subclass, it should not return -- it
         should either exit or raise an exception.
         """
         self.print_usage(_sys.stderr)
         self.exit(2, _('%s: error: %s\n') % (self.prog, message))