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argparse.py
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2786 lines (2319 loc) · 104 KB
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# Author: Steven J. Bethard <steven.bethard@gmail.com>.
# New maintainer as of 29 August 2019: Raymond Hettinger <raymond.hettinger@gmail.com>
"""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',
help='the file where the sum should be written')
args = parser.parse_args()
with (open(args.log, 'w') if args.log is not None
else contextlib.nullcontext(sys.stdout)) as log:
log.write('%s' % sum(args.integers))
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. Deprecated since
Python 3.14.
- 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__ = '1.1'
__all__ = [
'ArgumentParser',
'ArgumentError',
'ArgumentTypeError',
'BooleanOptionalAction',
'FileType',
'HelpFormatter',
'ArgumentDefaultsHelpFormatter',
'RawDescriptionHelpFormatter',
'RawTextHelpFormatter',
'MetavarTypeHelpFormatter',
'Namespace',
'Action',
'ONE_OR_MORE',
'OPTIONAL',
'PARSER',
'REMAINDER',
'SUPPRESS',
'ZERO_OR_MORE',
]
import os as _os
import re as _re
import sys as _sys
from gettext import gettext as _, ngettext
SUPPRESS = '==SUPPRESS=='
OPTIONAL = '?'
ZERO_OR_MORE = '*'
ONE_OR_MORE = '+'
PARSER = 'A...'
REMAINDER = '...'
_UNRECOGNIZED_ARGS_ATTR = '_unrecognized_args'
# =============================
# 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 = []
star_args = {}
for arg in self._get_args():
arg_strings.append(repr(arg))
for name, value in self._get_kwargs():
if name.isidentifier():
arg_strings.append('%s=%r' % (name, value))
else:
star_args[name] = value
if star_args:
arg_strings.append('**%s' % repr(star_args))
return '%s(%s)' % (type_name, ', '.join(arg_strings))
def _get_kwargs(self):
return list(self.__dict__.items())
def _get_args(self):
return []
def _copy_items(items):
if items is None:
return []
# The copy module is used only in the 'append' and 'append_const'
# actions, and it is needed only when the default value isn't a list.
# Delay its import for speeding up the common case.
if type(items) is list:
return items[:]
import copy
return copy.copy(items)
def _identity(value):
return value
# ===============
# 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,
color=True,
):
# default setting for width
if width is None:
import shutil
width = shutil.get_terminal_size().columns
width -= 2
self._set_color(color)
self._prog = prog
self._indent_increment = indent_increment
self._max_help_position = min(max_help_position,
max(width - 20, indent_increment * 2))
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+', _re.ASCII)
self._long_break_matcher = _re.compile(r'\n\n\n+')
def _set_color(self, color):
from _colorize import can_colorize, decolor, get_theme
if color and can_colorize():
self._theme = get_theme(force_color=True).argparse
self._decolor = decolor
else:
self._theme = get_theme(force_no_color=True).argparse
self._decolor = _identity
# ===============================
# 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
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_text = _('%(heading)s:') % dict(heading=self.heading)
t = self.formatter._theme
heading = (
f'{" " * current_indent}'
f'{t.heading}{heading_text}{t.reset}\n'
)
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 = lambda x: self._decolor(self._format_action_invocation(x))
invocation_lengths = [len(get_invocation(action)) + self._current_indent]
for subaction in self._iter_indented_subactions(action):
invocation_lengths.append(len(get_invocation(subaction)) + self._current_indent)
# update the maximum item length
action_length = max(invocation_lengths)
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):
t = self._theme
if prefix is None:
prefix = _('usage: ')
# if usage is specified, use that
if usage is not None:
usage = (
t.prog_extra
+ usage
% {"prog": f"{t.prog}{self._prog}{t.reset}{t.prog_extra}"}
+ t.reset
)
# if no optionals or positionals are available, usage is just prog
elif usage is None and not actions:
usage = f"{t.prog}{self._prog}{t.reset}"
# if optionals and positionals are available, calculate usage
elif usage is None:
prog = '%(prog)s' % dict(prog=self._prog)
parts, pos_start = self._get_actions_usage_parts(actions, groups)
# build full usage string
usage = ' '.join(filter(None, [prog, *parts]))
# wrap the usage parts if it's too long
text_width = self._width - self._current_indent
if len(prefix) + len(self._decolor(usage)) > text_width:
# break usage into wrappable parts
opt_parts = parts[:pos_start]
pos_parts = parts[pos_start:]
# helper for wrapping lines
def get_lines(parts, indent, prefix=None):
lines = []
line = []
indent_length = len(indent)
if prefix is not None:
line_len = len(prefix) - 1
else:
line_len = indent_length - 1
for part in parts:
part_len = len(self._decolor(part))
if line_len + 1 + part_len > text_width and line:
lines.append(indent + ' '.join(line))
line = []
line_len = indent_length - 1
line.append(part)
line_len += part_len + 1
if line:
lines.append(indent + ' '.join(line))
if prefix is not None:
lines[0] = lines[0][indent_length:]
return lines
# if prog is short, follow it with optionals or positionals
prog_len = len(self._decolor(prog))
if len(prefix) + prog_len <= 0.75 * text_width:
indent = ' ' * (len(prefix) + prog_len + 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)
usage = usage.removeprefix(prog)
usage = f"{t.prog}{prog}{t.reset}{usage}"
# prefix with 'usage:'
return f'{t.usage}{prefix}{t.reset}{usage}\n\n'
def _is_long_option(self, string):
return len(string) > 2
def _get_actions_usage_parts(self, actions, groups):
"""Get usage parts with split index for optionals/positionals.
Returns (parts, pos_start) where pos_start is the index in parts
where positionals begin.
This preserves mutually exclusive group formatting across the
optionals/positionals boundary (gh-75949).
"""
actions = [action for action in actions if action.help is not SUPPRESS]
# group actions by mutually exclusive groups
action_groups = dict.fromkeys(actions)
for group in groups:
for action in group._group_actions:
if action in action_groups:
action_groups[action] = group
# positional arguments keep their position
positionals = []
for action in actions:
if not action.option_strings:
group = action_groups.pop(action)
if group:
group_actions = [
action2 for action2 in group._group_actions
if action2.option_strings and
action_groups.pop(action2, None)
] + [action]
positionals.append((group.required, group_actions))
else:
positionals.append((None, [action]))
# the remaining optional arguments are sorted by the position of
# the first option in the group
optionals = []
for action in actions:
if action.option_strings and action in action_groups:
group = action_groups.pop(action)
if group:
group_actions = [action] + [
action2 for action2 in group._group_actions
if action2.option_strings and
action_groups.pop(action2, None)
]
optionals.append((group.required, group_actions))
else:
optionals.append((None, [action]))
# collect all actions format strings
parts = []
t = self._theme
pos_start = None
for i, (required, group) in enumerate(optionals + positionals):
start = len(parts)
if i == len(optionals):
pos_start = start
in_group = len(group) > 1
for action in group:
# produce all arg strings
if not action.option_strings:
default = self._get_default_metavar_for_positional(action)
part = self._format_args(action, default)
# if it's in a group, strip the outer []
if in_group:
if part[0] == '[' and part[-1] == ']':
part = part[1:-1]
part = t.summary_action + part + t.reset
# produce the first way to invoke the option in brackets
else:
option_string = action.option_strings[0]
if self._is_long_option(option_string):
option_color = t.summary_long_option
else:
option_color = t.summary_short_option
# if the Optional doesn't take a value, format is:
# -s or --long
if action.nargs == 0:
part = action.format_usage()
part = f"{option_color}{part}{t.reset}"
# if the Optional takes a value, format is:
# -s ARGS or --long ARGS
else:
default = self._get_default_metavar_for_optional(action)
args_string = self._format_args(action, default)
part = (
f"{option_color}{option_string} "
f"{t.summary_label}{args_string}{t.reset}"
)
# make it look optional if it's not required or in a group
if not (action.required or required or in_group):
part = '[%s]' % part
# add the action string to the list
parts.append(part)
if in_group:
parts[start] = ('(' if required else '[') + parts[start]
for i in range(start, len(parts) - 1):
parts[i] += ' |'
parts[-1] += ')' if required else ']'
if pos_start is None:
pos_start = len(parts)
return parts, pos_start
def _format_text(self, text):
if '%(prog)' in text:
text = text % dict(prog=self._prog)
text_width = max(self._width - self._current_indent, 11)
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 = max(self._width - help_position, 11)
action_width = help_position - self._current_indent - 2
action_header = self._format_action_invocation(action)
action_header_no_color = self._decolor(action_header)
# no help; 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_no_color) <= action_width:
# calculate widths without color codes
action_header_color = action_header
tup = self._current_indent, '', action_width, action_header_no_color
action_header = '%*s%-*s ' % tup
# swap in the colored header
action_header = action_header.replace(
action_header_no_color, action_header_color
)
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 and action.help.strip():
help_text = self._expand_help(action)
if help_text:
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):
t = self._theme
if not action.option_strings:
default = self._get_default_metavar_for_positional(action)
return (
t.action
+ ' '.join(self._metavar_formatter(action, default)(1))
+ t.reset
)
else:
def color_option_strings(strings):
parts = []
for s in strings:
if self._is_long_option(s):
parts.append(f"{t.long_option}{s}{t.reset}")
else:
parts.append(f"{t.short_option}{s}{t.reset}")
return parts
# if the Optional doesn't take a value, format is:
# -s, --long
if action.nargs == 0:
option_strings = color_option_strings(action.option_strings)
return ', '.join(option_strings)
# if the Optional takes a value, format is:
# -s, --long ARGS
else:
default = self._get_default_metavar_for_optional(action)
option_strings = color_option_strings(action.option_strings)
args_string = (
f"{t.label}{self._format_args(action, default)}{t.reset}"
)
return ', '.join(option_strings) + ' ' + args_string
def _metavar_formatter(self, action, default_metavar):
if action.metavar is not None:
result = action.metavar
elif action.choices is not None:
result = '{%s}' % ','.join(map(str, action.choices))
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:
metavar = get_metavar(1)
if len(metavar) == 2:
result = '[%s [%s ...]]' % metavar
else:
result = '[%s ...]' % metavar
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)
elif action.nargs == SUPPRESS:
result = ''
else:
try:
formats = ['%s' for _ in range(action.nargs)]
except TypeError:
raise ValueError("invalid nargs value") from None
result = ' '.join(formats) % get_metavar(action.nargs)
return result
def _expand_help(self, action):
help_string = self._get_help_string(action)
if '%' not in help_string:
return help_string
params = dict(vars(action), prog=self._prog)
for name in list(params):
value = params[name]
if value is SUPPRESS:
del params[name]
elif hasattr(value, '__name__'):
params[name] = value.__name__
if params.get('choices') is not None:
params['choices'] = ', '.join(map(str, params['choices']))
return help_string % params
def _iter_indented_subactions(self, action):
try:
get_subactions = action._get_subactions
except AttributeError:
pass
else:
self._indent()
yield from get_subactions()
self._dedent()
def _split_lines(self, text, width):
text = self._whitespace_matcher.sub(' ', text).strip()
# The textwrap module is used only for formatting help.
# Delay its import for speeding up the common usage of argparse.
import textwrap
return textwrap.wrap(text, width)
def _fill_text(self, text, width, indent):
text = self._whitespace_matcher.sub(' ', text).strip()
import textwrap
return textwrap.fill(text, width,
initial_indent=indent,
subsequent_indent=indent)
def _get_help_string(self, action):
return action.help
def _get_default_metavar_for_optional(self, action):
return action.dest.upper()
def _get_default_metavar_for_positional(self, action):
return action.dest
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(keepends=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 help is None:
help = ''
if (
'%(default)' not in help
and action.default is not SUPPRESS
and not action.required
):
defaulting_nargs = (OPTIONAL, ZERO_OR_MORE)
if action.option_strings or action.nargs in defaulting_nargs:
help += _(' (default: %(default)s)')
return help
class MetavarTypeHelpFormatter(HelpFormatter):
"""Help message formatter which uses the argument 'type' as the default
metavar value (instead of the argument 'dest')
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_default_metavar_for_optional(self, action):
return action.type.__name__
def _get_default_metavar_for_positional(self, action):
return action.type.__name__
# =====================
# 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):
metavar = argument.metavar
if not isinstance(metavar, tuple):
return metavar
if argument.nargs == ZERO_OR_MORE and len(metavar) == 2:
return '%s[, %s]' % metavar
elif argument.nargs == ONE_OR_MORE:
return '%s[, %s]' % metavar
else:
return ', '.join(metavar)
elif argument.dest not in (None, SUPPRESS):
return argument.dest
elif argument.choices:
return '{%s}' % ','.join(map(str, argument.choices))
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 -- A callable that accepts a single string argument, and
returns the converted value. The standard Python types str, int,
float, and complex are useful examples of such callables. If None,
str is used.
- 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,
deprecated=False):
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
self.deprecated = deprecated
def _get_kwargs(self):
names = [
'option_strings',
'dest',
'nargs',
'const',
'default',
'type',
'choices',
'required',
'help',
'metavar',
'deprecated',
]
return [(name, getattr(self, name)) for name in names]
def format_usage(self):
return self.option_strings[0]
def __call__(self, parser, namespace, values, option_string=None):
raise NotImplementedError('.__call__() not defined')
class BooleanOptionalAction(Action):
def __init__(self,
option_strings,
dest,
default=None,
required=False,
help=None,
deprecated=False):
_option_strings = []
for option_string in option_strings:
_option_strings.append(option_string)
if option_string.startswith('--'):
if option_string.startswith('--no-'):
raise ValueError(f'invalid option name {option_string!r} '
f'for BooleanOptionalAction')
option_string = '--no-' + option_string[2:]
_option_strings.append(option_string)
super().__init__(
option_strings=_option_strings,
dest=dest,
nargs=0,
default=default,
required=required,
help=help,
deprecated=deprecated)
def __call__(self, parser, namespace, values, option_string=None):
if option_string in self.option_strings:
setattr(namespace, self.dest, not option_string.startswith('--no-'))
def format_usage(self):
return ' | '.join(self.option_strings)
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,
deprecated=False):
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,
deprecated=deprecated)
def __call__(self, parser, namespace, values, option_string=None):
setattr(namespace, self.dest, values)