Available functions

For a quick reference, below there is a summary for all parameters of the function arg(), the dataparser() decorator and the function subparser():

Additional parameters for the arg() function:

Name	Quick description
`name_or_flags`	A list of option strings, starting with `-`.
`group`	A previously defined `ClassVar` using function `group()`
`mutually_exclusive_group`	A previously defined `ClassVar` using function `mutually_exclusive_group()`
`group_title`	The title (or a simple id integer) of the argument group
`mutually_exclusive_group_id`	The name (or a simple integer) of the mutually exclusive group
`make_flag`	Wether to force the automatic creation of a flag

Parameters of the original add_argument() method used in the arg() function:

Name	Quick description
`action`	The basic type of action to be taken
`nargs`	The number of command-line arguments that should be consumed
`const`	A constant value required by some action and nargs selections
`default`	The value produced if the argument is absent from the command line
`type`	The type to which the command-line argument should be converted
`choices`	A sequence of the allowable values for the argument
`required`	Whether or not the command-line option may be omitted
`help`	A brief description of what the argument does
`metavar`	A name for the argument in usage messages.
`dest`	The name of the attribute to be added to the object returned (not used)

Additional parameters for the dataparser() decorator:

Name	Quick description
`groups_descriptions`	A dictionary with argument groups descriptions
`required_mutually_exclusive_groups`	A dictionary with booleans
`default_bool`	The default boolean value used in in boolean fields
`help_formatter`	A formatter function used to format the help text

Parameters of the original ArgumentParser constructor used in the dataparser() decorator:

Name	Quick description
`prog`	The name of the program
`usage`	The string describing the program usage
`description`	Text to display before the argument help
`epilog`	Text to display after the argument help
`parents`	A list of ArgumentParser objects
`formatter_class`	A class for customizing the help output
`prefix_chars`	The set of characters that prefix optional arguments
`fromfile_prefix_chars`	The set of characters
`argument_default`	The global default value for arguments
`conflict_handler`	The strategy for resolving conflicting optionals
`add_help`	Add a `-h/--help` option to the parser
`allow_abbrev`	Allows long options to be abbreviated
`exit_on_error`	Determines whether or not ArgumentParser exits with error

Additional parameters for the subparser() function:

Name	Quick description
`defaults`	A dictionary with subparser level default attribute values

Parameters of the original add_parser() method used in the subparser() function:

Name	Quick description
`aliases`	An additional argument which allows multiple strings to refer to the same subparser
`help`	A help message for the subparser command

Note: add_parser() accepts all kwargs of ArgumentParser constructor. It also accepts its own help and aliases kwargs.

Helper function to create dataclass() fields storing specification about arguments, used later in the method add_argument().

This function accepts all parameters of the original add_argument() method (except for dest). Three additional parameters may be supplied, namely group_title, mutually_exclusive_group_id and make_flag. The parameter name_or_flags, taken from the original add_argument() method, behaves a little different.

Parameters

name_or_flags (str):

A list of option strings, e.g. -f, --foo, i.e., starting with -.

The first arguments passed to arg() must be a series of flags, or empty (not pass). It is not possible to pass a simple argument name to identify positional arguments. In that case, that name is already taken from the dataclass field name. This is the only argument taken from the original add_argument() method which behavior differs from its original behavior.

In some particular cases, flag name starting with -- may be automatically created from the dataclass field name even when name_or_flags is not given. See the make_flag argument for details.
group (Field[Any] | str | int | None, optional): Defaults to None.
A previously defined ClassVar field name using the function group(), or the title (or a simple id integer) of the argument group in which the argument may be added.

This is the best way to use the functionality of the method add_argument_group() of the standard ArgumentParser class:
@dataclass
class Args:
    my_first_group: ClassVar = group()
    foo: str = arg(group=my_first_group)
    bar: str = arg(group=my_first_group)

    my_second_group: ClassVar = group()
    sam: str = arg(group=my_second_group)
    ham: str = arg(group=my_second_group)
By default, ArgumentParser groups command-line arguments into “positional arguments” and “options” when displaying help messages. When there is a better conceptual grouping of arguments than this default one, appropriate groups can be created using the add_argument_group() method, that accepts title and description parameters, which can be used to customize the help display.

To define the title and description of the argument group, see the group() function used to define the ClassVar. When a string is passed to the group keyword argument, it is associated to the group title.
mutually_exclusive_group (Field[Any] | str | int | None, optional): Defaults to None.
A previously defined ClassVar field name using the function mutually_exclusive_group(), or a string or a simple id integer identifying the mutually exclusive group in which the argument may be included.

This parameter will make sure that only one of the arguments included in the mutually exclusive group ID is present on the command line:
>>> from dataclasses import dataclass
>>> from dataparsers import arg, mutually_exclusive_group, make_parser, parse
>>> from typing import ClassVar
>>>
>>> @dataclass
... class Args:
...     my_group: ClassVar = mutually_exclusive_group()
...     foo: str = arg(mutually_exclusive_group=my_group)
...     bar: str = arg(mutually_exclusive_group=my_group)
...
>>> make_parser(Args).print_help()
usage: [-h] [--foo FOO | --bar BAR]

options:
  -h, --help  show this help message and exit
  --foo FOO
  --bar BAR
>>>
>>> parse(Args, ["--foo", "test", "--bar", "newtest"])
usage: [-h] [--foo FOO | --bar BAR]
: error: argument --bar: not allowed with argument --foo
This is the best way to use the functionality of the method add_mutually_exclusive_group() of the standard ArgumentParser class.

The original add_mutually_exclusive_group() method also accepts a required parameter, to indicate that at least one of the mutually exclusive arguments is required. To define the required parameter of the mutually exclusive argument group, see the mutually_exclusive_group() function used to define the ClassVar.

Note:
Mutually exclusive are always optionals. If no flag is given, it will be created automatically from the dataclass() field name, regardless of the value of make_flag.
subparser (Field[Any] | None, optional): Defaults to None.
A previously defined ClassVar field name using the function subparser(), denoting the name of the subparser to which the argument will be added. If None (the default) the argument will be added to the main parser.

This is quick way to use the functionality of the method add_parser() of the action object returned by the add_subparsers() method:
>>> from typing import ClassVar
>>> from dataparsers import dataparser, arg, subparser, parse
>>>
>>> @dataparser(prog="PROG")
... class Args:
...     foo: bool = arg(help="foo help")
...     ...
...     a: ClassVar = subparser(help="a help")
...     bar: int = arg(help="bar help", subparser=a)
...     ...
...     b: ClassVar = subparser(help="b help")
...     baz: str = arg(make_flag=True, choices="XYZ", help="baz help", subparser=b)
...
>>> parse(Args, ["a", "12"])
Args(foo=False, bar=12, baz=None)
>>> parse(Args, ["--foo", "b", "--baz", "Z"])
Args(foo=True, bar=None, baz='Z')
The original add_parser() method also accepts all ArgumentParser constructor arguments. To define these arguments see the subparser() function used to define the ClassVar.
group_title (str | int | None, optional): Defaults to None.
Note:
This argument is kept to maintain compatibility with version prior to v2.1, and may be removed in the future. A better way to define argument groups is using the group keyword argument.

The title (or a simple id integer) of the argument group in which the argument may be added.

This is quick way to use the functionality of the method add_argument_group() of the standard ArgumentParser class.

By default, ArgumentParser groups command-line arguments into “positional arguments” and “options” when displaying help messages. When there is a better conceptual grouping of arguments than this default one, appropriate groups can be created using the add_argument_group() method, that accepts title and description parameters, which can be used to customize the help display.

The group_title parameter identifies the title of the argument group to include the argument:
>>> @dataclass
... class Args:
...     foo: str = arg(group_title="my group", help="foo help", make_flag=True)
...     bar: str = arg(group_title="my group", help="bar help")
...
>>> parser = make_parser(Args)
>>> parser.print_help()
usage: [-h] [--foo FOO] bar

options:
  -h, --help  show this help message and exit

my group:
  --foo FOO   foo help
  bar         bar help
To define the description of the argument group, see the dataparser() decorator.
mutually_exclusive_group_id (str | int | None, optional): Defaults to None.
Note:
This argument is kept to maintain compatibility with version prior to v2.1, and may be removed in the future. A better way to define mutually exclusive argument groups is using the mutually_exclusive_group keyword argument.

The name (or a simple integer) that is used as an ID of the a mutually exclusive group in which the argument may be included.

This parameter will make sure that only one of the arguments included in the mutually exclusive group ID is present on the command line:
>>> @dataclass
... class Args:
...     foo: bool = arg(action="store_true", mutually_exclusive_group_id="my_group")
...     bar: bool = arg(action="store_false", mutually_exclusive_group_id="my_group")
...
>>> parse(Args, ["--foo"])
Args(foo=True, bar=True)
>>> parse(Args, ["--bar"])
Args(foo=False, bar=False)
>>> parse(Args, ["--foo", "--bar"])
usage: [-h] [--foo | --bar]
: error: argument --bar: not allowed with argument --foo
This is a way to use the functionality of the method add_mutually_exclusive_group() of the standard argparse.ArgumentParser class.

The original add_mutually_exclusive_group() method also accepts a required parameter, to indicate that at least one of the mutually exclusive arguments is required. To define the required parameter of the mutually exclusive argument group, see the dataparser() decorator.

Note:
Mutually exclusive are always optionals. If no flag is given, it will be created automatically from the dataclass() field name, regardless of the value of make_flag.
make_flag (bool | None, optional): Defaults to None.
Wether to force the automatic creation of a flag starting with -- from the field name.

In general, the default keyword argument automatically makes the argument optional (i.e., creates a -- flag), but there are some situation when that doesn’t happen, e.g., when the parameter nargs is passed and set equal to ? or *. To force the automatic -- flag creation in theses cases, pass make_flag=True.

I general, flag name starting with -- may be automatically created from the dataclass field name even when name_or_flags is not given:
If default value is given (with nargs not equal to ? or *):
>>> @dataclass
... class Arg:
...     foo: str = arg(default=42)
...     bar: int = arg()
...
>>>
>>> parser = make_parse(Arg)
>>> parser.print_help()
usage: [-h] [--foo FOO] bar

positional arguments:
  bar

options:
  -h, --help  show this help message and exit
  --foo FOO
If only single flags are given (i.e., starting with - but none with --):
>>> @dataclass
... class Arg:
...     foo: str = arg("-f")
...     bar: str = arg("-b")
...
>>>
>>> parser = make_parse(Arg)
>>> parser.print_help()
usage: [-h] [-f FOO] [-b BAR]

options:
  -h, --help         show this help message and exit
  -f FOO, --foo FOO
  -b BAR, --bar BAR
To prevent the automatic creation of the flag in these cases, pass make_flag=False.

Parameters from the original `add_argument()` method

action (Literal["store", "store_const", "store_true", "store_false", "append", "append_const", "count", "help", "version", "extend"] | type[Action], optional): Defaults to "store".
The basic type of action to be taken when this argument is encountered at the command line.

ArgumentParser objects associate command-line arguments with actions. These actions can do just about anything with the command-line arguments associated with them, though most actions simply add an attribute to the object returned by parse_args(). The action keyword argument specifies how the command-line arguments should be handled. The supplied actions are
"store": This just stores the argument’s value. This is the default action. For example:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo')
>>> parser.parse_args('--foo 1'.split())
Namespace(foo='1')
"store_const": This stores the value specified by the const keyword argument; note that the const keyword argument defaults to None. The store_const action is most commonly used with optional arguments that specify some sort of flag. For example:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='store_const', const=42)
>>> parser.parse_args(['--foo'])
Namespace(foo=42)
"store_true" and "store_false" - These are special cases of "store_const" used for storing the values True and False respectively. In addition, they create default values of False and True respectively. For example:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='store_true')
>>> parser.add_argument('--bar', action='store_false')
>>> parser.add_argument('--baz', action='store_false')
>>> parser.parse_args('--foo --bar'.split())
Namespace(foo=True, bar=False, baz=True)
"append" - This stores a list, and appends each argument value to the list. It is useful to allow an option to be specified multiple times. If the default value is non-empty, the default elements will be present in the parsed value for the option, with any values from the command line appended after those default values. Example usage:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='append')
>>> parser.parse_args('--foo 1 --foo 2'.split())
Namespace(foo=['1', '2'])
"append_const" - This stores a list, and appends the value specified by the const keyword argument to the list; note that the const keyword argument defaults to None. The "append_const" action is typically useful when multiple arguments need to store constants to the same list. For example:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--str', dest='types', action='append_const', const=str)
>>> parser.add_argument('--int', dest='types', action='append_const', const=int)
>>> parser.parse_args('--str --int'.split())
Namespace(types=[<class 'str'>, <class 'int'>])
"count" - This counts the number of times a keyword argument occurs. For example, this is useful for increasing verbosity levels:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--verbose', '-v', action='count', default=0)
>>> parser.parse_args(['-vvv'])
Namespace(verbose=3)
Note, the default will be None unless explicitly set to 0.
"help" - This prints a complete help message for all the options in the current parser and then exits. By default a help action is automatically added to the parser. See ArgumentParser for details of how the output is created.
"version" - This expects a version= keyword argument in the add_argument() call, and prints version information and exits when invoked:
>>> import argparse
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('--version', action='version', version='%(prog)s 2.0')
>>> parser.parse_args(['--version'])
PROG 2.0
"extend" - This stores a list, and extends each argument value to the list. Example usage:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument("--foo", action="extend", nargs="+", type=str)
>>> parser.parse_args(["--foo", "f1", "--foo", "f2", "f3", "f4"])
Namespace(foo=['f1', 'f2', 'f3', 'f4'])
You may also specify an arbitrary action by passing an Action subclass or other object that implements the same interface. The BooleanOptionalAction is available in argparse and adds support for boolean actions such as --foo and --no-foo:
>>> import argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action=argparse.BooleanOptionalAction)
>>> parser.parse_args(['--no-foo'])
Namespace(foo=False)
The recommended way to create a custom action is to extend Action, overriding the __call__ method and optionally the __init__ and format_usage methods. An example of a custom action:
>>> class FooAction(argparse.Action):
...    def __init__(self, option_strings, dest, nargs=None, **kwargs):
...        if nargs is not None:
...            raise ValueError("nargs not allowed")
...        super().__init__(option_strings, dest, **kwargs)
...    def __call__(self, parser, namespace, values, option_string=None):
...        print('%r %r %r' % (namespace, values, option_string))
...        setattr(namespace, self.dest, values)
...
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action=FooAction)
>>> parser.add_argument('bar', action=FooAction)
>>> args = parser.parse_args('1 --foo 2'.split())
Namespace(bar=None, foo=None) '1' None
Namespace(bar='1', foo=None) '2' '--foo'
>>> args
Namespace(bar='1', foo='2')
For more details, see Action.
nargs (int | Literal["?", "*", "+"], optional): Defaults to None.
The number of command-line arguments that should be consumed.

ArgumentParser objects usually associate a single command-line argument with a single action to be taken. The nargs keyword argument associates a different number of command-line arguments with a single action. See also “Specifying ambiguous arguments”. The supported values are:
N (an integer) - N arguments from the command line will be gathered together into a list. For example:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', nargs=2)
>>> parser.add_argument('bar', nargs=1)
>>> parser.parse_args('c --foo a b'.split())
Namespace(bar=['c'], foo=['a', 'b'])
Note that nargs=1 produces a list of one item. This is different from the default, in which the item is produced by itself.
"?" - One argument will be consumed from the command line if possible, and produced as a single item. If no command-line argument is present, the value from default will be produced. Note that for optional arguments, there is an additional case - the option string is present but not followed by a command-line argument. In this case the value from const will be produced. Some examples to illustrate this:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', nargs='?', const='c', default='d')
>>> parser.add_argument('bar', nargs='?', default='d')
>>> parser.parse_args(['XX', '--foo', 'YY'])
Namespace(bar='XX', foo='YY')
>>> parser.parse_args(['XX', '--foo'])
Namespace(bar='XX', foo='c')
>>> parser.parse_args([])
Namespace(bar='d', foo='d')
One of the more common uses of nargs="?" is to allow optional input and output files:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('infile', nargs='?', type=argparse.FileType('r'), default=sys.stdin)
>>> parser.add_argument('outfile', nargs='?', type=argparse.FileType('w'), default=sys.stdout)
>>> parser.parse_args(['input.txt', 'output.txt'])
Namespace(infile=<_io.TextIOWrapper name='input.txt' encoding='UTF-8'>,
        outfile=<_io.TextIOWrapper name='output.txt' encoding='UTF-8'>)
>>> parser.parse_args([])
Namespace(infile=<_io.TextIOWrapper name='<stdin>' encoding='UTF-8'>,
        outfile=<_io.TextIOWrapper name='<stdout>' encoding='UTF-8'>)
"*" - All command-line arguments present are gathered into a list. Note that it generally doesn’t make much sense to have more than one positional argument with nargs="*", but multiple optional arguments with nargs="*" is possible. For example:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', nargs='*')
>>> parser.add_argument('--bar', nargs='*')
>>> parser.add_argument('baz', nargs='*')
>>> parser.parse_args('a b --foo x y --bar 1 2'.split())
Namespace(bar=['1', '2'], baz=['a', 'b'], foo=['x', 'y']
"+" - Just like "*", all command-line args present are gathered into a list. Additionally, an error message will be generated if there wasn’t at least one command-line argument present. For example:
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('foo', nargs='+')
>>> parser.parse_args(['a', 'b'])
Namespace(foo=['a', 'b'])
>>> parser.parse_args([])
usage: PROG [-h] foo [foo ...]
PROG: error: the following arguments are required: foo
const (Any | None, optional): Defaults to None.

A constant value required by some action and nargs selections.

The const argument of add_argument() is used to hold constant values that are not read from the command line but are required for the various ArgumentParser actions. The two most common uses of it are:

(1) When add_argument() is called with action='store_const' or action='append_const'. These actions add the const value to one of the attributes of the object returned by parse_args(). See the action description for examples. If const is not provided to add_argument(), it will receive a default value of None.

(2) When add_argument() is called with option strings (like -f or --foo) and nargs='?'. This creates an optional argument that can be followed by zero or one command-line arguments. When parsing the command line, if the option string is encountered with no command-line argument following it, the value of const will be assumed to be None instead. See the nargs description for examples.

Changed in version 3.11: const=None by default, including when action='append_const' or action='store_const'.
default (Any, optional): Defaults to None.
The value produced if the argument is absent from the command line and if it is absent from the namespace object.

All optional arguments and some positional arguments may be omitted at the command line. The default keyword argument of add_argument(), whose value defaults to None, specifies what value should be used if the command-line argument is not present. For optional arguments, the default value is used when the option string was not present at the command line:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', default=42)
>>> parser.parse_args(['--foo', '2'])
Namespace(foo='2')
>>> parser.parse_args([])
Namespace(foo=42)
If the target namespace already has an attribute set, the action default will not over write it:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', default=42)
>>> parser.parse_args([], namespace=argparse.Namespace(foo=101))
Namespace(foo=101)
If the default value is a string, the parser parses the value as if it were a command-line argument. In particular, the parser applies any type conversion argument, if provided, before setting the attribute on the Namespace return value. Otherwise, the parser uses the value as is:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--length', default='10', type=int)
>>> parser.add_argument('--width', default=10.5, type=int)
>>> parser.parse_args()
Namespace(length=10, width=10.5)
For positional arguments with nargs equal to ? or *, the default value is used when no command-line argument was present:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('foo', nargs='?', default=42)
>>> parser.parse_args(['a'])
Namespace(foo='a')
>>> parser.parse_args([])
Namespace(foo=42)
Note:
Giving some default value to the function arg() will force the argument to be optional if there is no flag present in the name_or_flags argument. That gives the same result as if make_flag=True. The only exception occurs when nargs is passed and it is equal to ? or *. In those cases, passing a default value will not force the argument to be optional. To achieve that, a flag must be passed in name_or_flags argument or explicit passing make_flag=True.

Providing default=argparse.SUPPRESS causes no attribute to be added if the command-line argument was not present:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', default=argparse.SUPPRESS)
>>> parser.parse_args([])
Namespace()
>>> parser.parse_args(['--foo', '1'])
Namespace(foo='1')
type (Callable[[str], T] | FileType | None, optional): Defaults to None.
Note:
If not given in the arg() function, the type parameter is automatically inferred from the dataclass field type, except for the case when the field type is bool (following recommendation below).

The type to which the command-line argument should be converted.

By default, the parser reads command-line arguments in as simple strings. However, quite often the command-line string should instead be interpreted as another type, such as a float or int. The type keyword for add_argument() allows any necessary type-checking and type conversions to be performed.

If the type keyword is used with the default keyword, the type converter is only applied if the default is a string.

The argument to type can be any callable that accepts a single string. If the function raises ArgumentTypeError, TypeError, or ValueError, the exception is caught and a nicely formatted error message is displayed. No other exception types are handled.

Common built-in types and functions can be used as type converters:
import argparse
import pathlib

parser = argparse.ArgumentParser()
parser.add_argument('count', type=int)
parser.add_argument('distance', type=float)
parser.add_argument('street', type=ascii)
parser.add_argument('code_point', type=ord)
parser.add_argument('source_file', type=open)
parser.add_argument('dest_file', type=argparse.FileType('w', encoding='latin-1'))
parser.add_argument('datapath', type=pathlib.Path)
User defined functions can be used as well:
>>> def hyphenated(string):
...    return '-'.join([word[:4] for word in string.casefold().split()])
...
>>> parser = argparse.ArgumentParser()
>>> _ = parser.add_argument('short_title', type=hyphenated)
>>> parser.parse_args(['"The Tale of Two Cities"'])
Namespace(short_title='"the-tale-of-two-citi')
The bool() function is not recommended as a type converter. All it does is convert empty strings to False and non-empty strings to True. This is usually not what is desired.

In general, the type keyword is a convenience that should only be used for simple conversions that can only raise one of the three supported exceptions. Anything with more interesting error-handling or resource management should be done downstream after the arguments are parsed.

For example, JSON or YAML conversions have complex error cases that require better reporting than can be given by the type keyword. A JSONDecodeError would not be well formatted and a FileNotFoundError exception would not be handled at all.

Even FileType has its limitations for use with the type keyword. If one argument uses FileType and then a subsequent argument fails, an error is reported but the file is not automatically closed. In this case, it would be better to wait until after the parser has run and then use the with-statement to manage the files.

For type checkers that simply check against a fixed set of values, consider using the choices keyword instead.
choices (Iterable[T] | None, optional): Defaults to None.
A sequence of the allowable values for the argument.

Some command-line arguments should be selected from a restricted set of values. These can be handled by passing a sequence object as the choices keyword argument to add_argument(). When the command line is parsed, argument values will be checked, and an error message will be displayed if the argument was not one of the acceptable values:
>>> parser = argparse.ArgumentParser(prog='game.py')
>>> parser.add_argument('move', choices=['rock', 'paper', 'scissors'])
>>> parser.parse_args(['rock'])
Namespace(move='rock')
>>> parser.parse_args(['fire'])
usage: game.py [-h] {rock,paper,scissors}
game.py: error: argument move: invalid choice: 'fire' (choose from 'rock',
'paper', 'scissors')
Note that inclusion in the choices sequence is checked after any type conversions have been performed, so the type of the objects in the choices sequence should match the type specified:
>>> parser = argparse.ArgumentParser(prog='doors.py')
>>> parser.add_argument('door', type=int, choices=range(1, 4))
>>> print(parser.parse_args(['3']))
Namespace(door=3)
>>> parser.parse_args(['4'])
usage: doors.py [-h] {1,2,3}
doors.py: error: argument door: invalid choice: 4 (choose from 1, 2, 3)
Any sequence can be passed as the choices value, so list objects, tuple objects, and custom sequences are all supported.

Use of enum.Enum is not recommended because it is difficult to control its appearance in usage, help, and error messages.

Formatted choices override the default metavar which is normally derived from dest. This is usually what you want because the user never sees the dest parameter. If this display isn’t desirable (perhaps because there are many choices), just specify an explicit metavar.
required (bool | None, optional): Defaults to None.
Whether or not the command-line option may be omitted (optionals only).

In general, the argparse module assumes that flags like -f and --bar indicate optional arguments, which can always be omitted at the command line. To make an option required, True can be specified for the required= keyword argument to add_argument():
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', required=True)
>>> parser.parse_args(['--foo', 'BAR'])
Namespace(foo='BAR')
>>> parser.parse_args([])
usage: [-h] --foo FOO
: error: the following arguments are required: --foo
As the example shows, if an option is marked as required, parse_args() will report an error if that option is not present at the command line.

Note:
Required options are generally considered bad form because users expect options to be optional, and thus they should be avoided when possible.
help (str | None, optional): Defaults to None.
A brief description of what the argument does.

The help value is a string containing a brief description of the argument. When a user requests help (usually by using -h or --help at the command line), these help descriptions will be displayed with each argument:
>>> parser = argparse.ArgumentParser(prog='frobble')
>>> parser.add_argument('--foo', action='store_true', help='foo the bars before frobbling')
>>> parser.add_argument('bar', nargs='+', help='one of the bars to be frobbled')
>>> parser.parse_args(['-h'])
usage: frobble [-h] [--foo] bar [bar ...]

positional arguments:
bar     one of the bars to be frobbled

options:
  -h, --help  show this help message and exit
  --foo   foo the bars before frobbling
The help strings can include various format specifiers to avoid repetition of things like the program name or the argument default. The available specifiers include the program name, %(prog)s and most keyword arguments to add_argument(), e.g. %(default)s, %(type)s, etc.:
>>> parser = argparse.ArgumentParser(prog='frobble')
>>> parser.add_argument('bar', nargs='?', type=int, default=42,
...                 help='the bar to %(prog)s (default: %(default)s)')
>>> parser.print_help()
usage: frobble [-h] [bar]

positional arguments:
bar     the bar to frobble (default: 42)

options:
  -h, --help  show this help message and exit
As the help string supports %-formatting, if you want a literal % to appear in the help string, you must escape it as %%.

argparse supports silencing the help entry for certain options, by setting the help value to argparse.SUPPRESS:
>>> parser = argparse.ArgumentParser(prog='frobble')
>>> parser.add_argument('--foo', help=argparse.SUPPRESS)
>>> parser.print_help()
usage: frobble [-h]

options:
  -h, --help  show this help message and exit
metavar (str | tuple[str, ...] | None, optional): Defaults to None.
A name for the argument in usage messages.

When ArgumentParser generates help messages, it needs some way to refer to each expected argument. By default, ArgumentParser objects use the dest value as the “name” of each object. By default, for positional argument actions, the dest value is used directly, and for optional argument actions, the dest value is uppercased. So, a single positional argument with dest='bar' will be referred to as bar. A single optional argument --foo that should be followed by a single command-line argument will be referred to as FOO. An example:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo')
>>> parser.add_argument('bar')
>>> parser.parse_args('X --foo Y'.split())
Namespace(bar='X', foo='Y')
>>> parser.print_help()
usage:  [-h] [--foo FOO] bar

positional arguments:
bar

options:
  -h, --help  show this help message and exit
  --foo FOO
An alternative name can be specified with metavar:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', metavar='YYY')
>>> parser.add_argument('bar', metavar='XXX')
>>> parser.parse_args('X --foo Y'.split())
Namespace(bar='X', foo='Y')
>>> parser.print_help()
usage:  [-h] [--foo YYY] XXX

positional arguments:
XXX

options:
  -h, --help  show this help message and exit
  --foo YYY
Note that metavar only changes the displayed name - the name of the attribute on the parse_args() object is still determined by the dest value.

Different values of nargs may cause the metavar to be used multiple times. Providing a tuple to metavar specifies a different display for each of the arguments:
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('-x', nargs=2)
>>> parser.add_argument('--foo', nargs=2, metavar=('bar', 'baz'))
>>> parser.print_help()
usage: PROG [-h] [-x X X] [--foo bar baz]

options:
  -h, --help     show this help message and exit
  -x X X
  --foo bar baz
dest (str | None, optional): Defaults to None.
Note:
The parameter dest is described here just for documentation. It will raise an error if it is passed to the arg() function, because it is not necessary: the dest keyword argument of the add_argument() method is taken from the dataclass field name.

The name of the attribute to be added to the object returned by parse_args().

Most ArgumentParser actions add some value as an attribute of the object returned by parse_args(). The name of this attribute is determined by the dest keyword argument of add_argument(). For positional argument actions, dest is normally supplied as the first argument to add_argument():
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('bar')
>>> parser.parse_args(['XXX'])
Namespace(bar='XXX')
For optional argument actions, the value of dest is normally inferred from the option strings. ArgumentParser generates the value of dest by taking the first long option string and stripping away the initial -- string. If no long option strings were supplied, dest will be derived from the first short option string by stripping the initial - character. Any internal - characters will be converted to _ characters to make sure the string is a valid attribute name. The examples below illustrate this behavior:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('-f', '--foo-bar', '--foo')
>>> parser.add_argument('-x', '-y')
>>> parser.parse_args('-f 1 -x 2'.split())
Namespace(foo_bar='1', x='2')
>>> parser.parse_args('--foo 1 -y 2'.split())
Namespace(foo_bar='1', x='2')
dest allows a custom attribute name to be provided:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', dest='bar')
>>> parser.parse_args('--foo XXX'.split())
Namespace(bar='XXX')

Returns

default@arg | Field: A dataclass() field with given default value of the field and metadata dictionary filled with argument parameters.

dataparsers.group( title: str | None = None, description: str | None = None, ) → Any[source]

Helper function to create dataclass() class variables (ClassVar) storing specification about argument groups, used later in the method add_argument_group().

This function accepts the parameters of the original add_argument_group() method, i.e., title and description, and must be used to define a ClassVar in the class scope.

Parameters

title (str | None, optional): Defaults to None.

The title of the argument group.

description (str | None, optional): Defaults to None.

The description of the argument group.

Returns

Field: A dataclass() field with metadata dictionary filled with argument group parameters, which must be assigned to a ClassVar field.

dataparsers.mutually_exclusive_group(*, required: bool = False) → Any[source]

Helper function to create dataclass() class variables (ClassVar) storing specification about mutually exclusive argument groups, used later in the method add_mutually_exclusive_group().

This function accepts the parameters of the original add_mutually_exclusive_group() method, i.e., required, and must be used to define a ClassVar in the class scope.

Parameters

required (bool, optional): Defaults to False.

Indicate that at least one of the mutually exclusive arguments is required.

Returns

Field: A dataclass() field with metadata dictionary filled with mutually exclusive argument group parameters, which must be assigned to a ClassVar field.

dataparsers.default(default: T | None = None) → T[source]

Helper function to create a dataclass() field storing a parser-level default, used later in the method set_defaults().

It allows some additional attributes to be stored without any inspection of the command line to be added.

Note

This function must be used prior to pass a dict value to the defaults keyword argument in the function subparser().

Parameters

default (T | None, optional): Defaults to None.

The stored default value of the attribute.

Returns

Field: A dataclass() field with the default attribute value stored in it.

dataparsers.dataparser( *, groups_descriptions: dict[str | int, str] | None = None, required_mutually_exclusive_groups: dict[str | int, bool] | None = None, default_bool: bool = False, help_formatter: Callable[[str], str] | None = None, prog: str | None = None, usage: str | None = None, description: str | None = None, epilog: str | None = None, parents: Sequence[ArgumentParser] = [], formatter_class: HelpFormatter = Ellipsis, prefix_chars: str = '-', fromfile_prefix_chars: str | None = None, argument_default: Any | None = None, conflict_handler: str = 'error', add_help: bool = True, allow_abbrev: bool = True, exit_on_error: bool = True, ) → Callable[[type[Class]], type[Class]][source]

A wrapper around dataclass() for passing parameters to the ArgumentParser constructor.

This function accepts all parameters of the original ArgumentParser constructor. Four additional parameters may be supplied, namely groups_descriptions, required_mutually_exclusive_groups, default_bool and help_formatter.

Parameters

groups_descriptions (dict[str | int, str] | None, optional): Defaults to None.

A dictionary with argument groups descriptions (used to customize the CLI display) whose keys should match some value of the argument group_title passed to the arg() function.

required_mutually_exclusive_groups (dict[str | int, bool] | None, optional): Defaults to None.

A dictionary with booleans indicating the required status of mutually exclusive groups arguments. The dictionary keys should match some value of the argument mutually_exclusive_group_id passed to the arg() function. The value True indicates that at least one of the mutually exclusive arguments in the matching group is required.

default_bool (bool, optional): Defaults to False.

The default boolean value used in in boolean fields when there is no default value passed.

help_formatter (Callable[[str], str] | None, optional): Defaults to None.

A formatter function used to format the help text in argument descriptions. When it is passed, the formatter_class parameter passed to the ArgumentParser constructor is assumed to be RawDescriptionHelpFormatter.

Parameters from the original `ArgumentParser` class

prog (str | None, optional): Defaults to None.
The name of the program (default: os.path.basename(sys.argv[0]))

By default, ArgumentParser objects use sys.argv[0] to determine how to display the name of the program in help messages. This default is almost always desirable because it will make the help messages match how the program was invoked on the command line. For example, consider a file named myprogram.py with the following code:
import argparse parser = argparse.ArgumentParser() parser.add_argument('--foo', help='foo help') args =
parser.parse_args()
The help for this program will display myprogram.py as the program name (regardless of where the program was invoked from):
$ python myprogram.py --help
usage: myprogram.py [-h] [--foo FOO]

options:
  -h, --help  show this help message and exit --foo FOO   foo help
$ cd .. $ python subdir/myprogram.py --help usage: myprogram.py [-h] [--foo FOO]

options:
  -h, --help  show this help message and exit --foo FOO   foo help
To change this default behavior, another value can be supplied using the prog= argument to ArgumentParser:
>>> parser = argparse.ArgumentParser(prog='myprogram')
>>> parser.print_help()
usage: myprogram [-h]

options:
  -h, --help  show this help message and exit
Note that the program name, whether determined from sys.argv[0] or from the prog= argument, is available to help messages using the %(prog)s format specifier:
>>> parser = argparse.ArgumentParser(prog='myprogram')
>>> parser.add_argument('--foo', help='foo of the %(prog)s program')
>>> parser.print_help()
usage: myprogram [-h] [--foo FOO]

options:
  -h, --help  show this help message and exit --foo FOO   foo of the myprogram program
usage (str | None, optional): Defaults to None.
The string describing the program usage (default: generated from arguments added to parser).

By default, ArgumentParser calculates the usage message from the arguments it contains:
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('--foo', nargs='?', help='foo help')
>>> parser.add_argument('bar', nargs='+', help='bar help')
>>> parser.print_help()
usage: PROG [-h] [--foo [FOO]] bar [bar ...]

positional arguments: bar          bar help

options:
  -h, --help   show this help message and exit --foo [FOO]  foo help
The default message can be overridden with the usage= keyword argument:
>>> parser = argparse.ArgumentParser(prog='PROG', usage='%(prog)s [options]')
>>> parser.add_argument('--foo', nargs='?', help='foo help')
>>> parser.add_argument('bar', nargs='+', help='bar help')
>>> parser.print_help()
usage: PROG [options]

positional arguments: bar          bar help

options:
  -h, --help   show this help message and exit --foo [FOO]  foo help
The %(prog)s format specifier is available to fill in the program name in your usage messages.
description (str | None, optional): Defaults to None.
Text to display before the argument help (by default, no text).

Most calls to the ArgumentParser constructor will use the description= keyword argument. This argument gives a brief description of what the program does and how it works. In help messages, the description is displayed between the command-line usage string and the help messages for the various arguments:
>>> parser = argparse.ArgumentParser(description='A foo that bars')
>>> parser.print_help()
usage: argparse.py [-h]

A foo that bars

options:
  -h, --help  show this help message and exit
By default, the description will be line-wrapped so that it fits within the given space. To change this behavior, see the formatter_class argument.
epilog (str | None, optional): Defaults to None.
Text to display after the argument help (by default, no text).

Some programs like to display additional description of the program after the description of the arguments. Such text can be specified using the epilog= argument to ArgumentParser:
>>> parser = argparse.ArgumentParser(
...                             description='A foo that bars', ... epilog="And that's how you'd foo a
bar") >>> parser.print_help() usage: argparse.py [-h]

A foo that bars

options:
  -h, --help  show this help message and exit

And that's how you'd foo a bar
As with the description argument, the epilog= text is by default line-wrapped, but this behavior can be adjusted with the formatter_class argument to ArgumentParser.
parents (Sequence[ArgumentParser], optional): Defaults to [].
A list of ArgumentParser objects whose arguments should also be included.

Sometimes, several parsers share a common set of arguments. Rather than repeating the definitions of these arguments, a single parser with all the shared arguments and passed to parents= argument to ArgumentParser can be used. The parents= argument takes a list of ArgumentParser objects, collects all the positional and optional actions from them, and adds these actions to the ArgumentParser object being constructed:
>>> parent_parser = argparse.ArgumentParser(add_help=False)
>>> parent_parser.add_argument('--parent', type=int)

>>> foo_parser = argparse.ArgumentParser(parents=[parent_parser])
>>> foo_parser.add_argument('foo')
>>> foo_parser.parse_args(['--parent', '2', 'XXX'])
Namespace(foo='XXX', parent=2)

>>> bar_parser = argparse.ArgumentParser(parents=[parent_parser])
>>> bar_parser.add_argument('--bar')
>>> bar_parser.parse_args(['--bar', 'YYY'])
Namespace(bar='YYY', parent=None)
Note that most parent parsers will specify add_help=False. Otherwise, the ArgumentParser will see two -h/--help options (one in the parent and one in the child) and raise an error.

Note:
You must fully initialize the parsers before passing them via parents=. If you change the parent parsers after the child parser, those changes will not be reflected in the child.
formatter_class (_FormatterClass, optional):
A class for customizing the help output.

ArgumentParser objects allow the help formatting to be customized by specifying an alternate formatting class. Currently, there are four such classes:
class argparse.RawDescriptionHelpFormatter
class argparse.RawTextHelpFormatter
class argparse.ArgumentDefaultsHelpFormatter
class argparse.MetavarTypeHelpFormatter
RawDescriptionHelpFormatter and RawTextHelpFormatter give more control over how textual descriptions are displayed. By default, ArgumentParser objects line-wrap the description and epilog texts in command-line help messages:
>>> parser = argparse.ArgumentParser(
...    prog='PROG',
...    description='''this description
...        was indented weird
...            but that is okay''',
...    epilog='''
...            likewise for this epilog whose whitespace will
...        be cleaned up and whose words will be wrapped
...        across a couple lines''')
>>> parser.print_help()
usage: PROG [-h]

this description was indented weird but that is okay

options:
 -h, --help  show this help message and exit

likewise for this epilog whose whitespace will be cleaned up and whose words
will be wrapped across a couple lines
Passing RawDescriptionHelpFormatter as formatter_class= indicates that description and epilog are already correctly formatted and should not be line-wrapped:
>>> parser = argparse.ArgumentParser(
...    prog='PROG',
...    formatter_class=argparse.RawDescriptionHelpFormatter,
...    description=textwrap.dedent('''                ...        Please do not mess up this text!
...        --------------------------------
...            I have indented it
...            exactly the way
...            I want it
...        '''))
>>> parser.print_help()
usage: PROG [-h]

Please do not mess up this text!
--------------------------------
   I have indented it
   exactly the way
   I want it

options:
 -h, --help  show this help message and exit
RawTextHelpFormatter maintains whitespace for all sorts of help text, including argument descriptions. However, multiple new lines are replaced with one. If you wish to preserve multiple blank lines, add spaces between the newlines.

ArgumentDefaultsHelpFormatter automatically adds information about default values to each of the argument help messages:
>>> parser = argparse.ArgumentParser(
...    prog='PROG',
...    formatter_class=argparse.ArgumentDefaultsHelpFormatter)
>>> parser.add_argument('--foo', type=int, default=42, help='FOO!')
>>> parser.add_argument('bar', nargs='*', default=[1, 2, 3], help='BAR!')
>>> parser.print_help()
usage: PROG [-h] [--foo FOO] [bar ...]

positional arguments:
 bar         BAR! (default: [1, 2, 3])

options:
 -h, --help  show this help message and exit
 --foo FOO   FOO! (default: 42)
MetavarTypeHelpFormatter uses the name of the type argument for each argument as the display name for its values (rather than using the dest as the regular formatter does):
>>> parser = argparse.ArgumentParser(
...     prog='PROG',
...     formatter_class=argparse.MetavarTypeHelpFormatter)
>>> parser.add_argument('--foo', type=int)
>>> parser.add_argument('bar', type=float)
>>> parser.print_help()
usage: PROG [-h] [--foo int] float

positional arguments:
  float

options:
  -h, --help  show this help message and exit
  --foo int
prefix_chars (str, optional): Defaults to "-".
The set of characters that prefix optional arguments (default: ‘-‘).

Most command-line options will use - as the prefix, e.g. -f/--foo. Parsers that need to support different or additional prefix characters, e.g. for options like +f or /foo, may specify them using the prefix_chars= argument to the ArgumentParser constructor:
>>> parser = argparse.ArgumentParser(prog='PROG', prefix_chars='-+')
>>> parser.add_argument('+f')
>>> parser.add_argument('++bar')
parser.parse_args('+f X ++bar Y'.split())
Namespace(bar='Y', f='X')
The prefix_chars= argument defaults to '-'. Supplying a set of characters that does not include - will cause -f/--foo options to be disallowed.
fromfile_prefix_chars (str | None, optional): Defaults to None.
The set of characters that prefix files from which additional arguments should be read (default: None).

Sometimes, when dealing with a particularly long argument list, it may make sense to keep the list of arguments in a file rather than typing it out at the command line. If the fromfile_prefix_chars= argument is given to the ArgumentParser constructor, then arguments that start with any of the specified characters will be treated as files, and will be replaced by the arguments they contain. For example:
>>> with open('args.txt', 'w', encoding=sys.getfilesystemencoding()) as fp:
...    fp.write('-f\nbar')
...
>>> parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
>>> parser.add_argument('-f')
>>> parser.parse_args(['-f', 'foo', '@args.txt'])
Namespace(f='bar')
Arguments read from a file must by default be one per line (but see also convert_arg_line_to_args()) and are treated as if they were in the same place as the original file referencing argument on the command line. So in the example above, the expression ['-f', 'foo', '@args.txt'] is considered equivalent to the expression ['-f', 'foo', '-f', 'bar'].

ArgumentParser uses filesystem encoding and error handler to read the file containing arguments.

The fromfile_prefix_chars= argument defaults to None, meaning that arguments will never be treated as file references.

Changed in version 3.12: ArgumentParser changed encoding and errors to read arguments files from default (e.g. locale.getpreferredencoding(False) and "strict") to filesystem encoding and error handler. Arguments file should be encoded in UTF-8 instead of ANSI Codepage on Windows.
argument_default (Any, optional): Defaults to None.
The global default value for arguments (default: None).

Generally, argument defaults are specified either by passing a default to add_argument() or by calling the set_defaults() methods with a specific set of name-value pairs. Sometimes however, it may be useful to specify a single parser-wide default for arguments. This can be accomplished by passing the argument_default= keyword argument to ArgumentParser. For example, to globally suppress attribute creation on parse_args() calls, we supply argument_default=SUPPRESS:
>>> parser = argparse.ArgumentParser(argument_default=argparse.SUPPRESS)
>>> parser.add_argument('--foo')
>>> parser.add_argument('bar', nargs='?')
>>> parser.parse_args(['--foo', '1', 'BAR'])
Namespace(bar='BAR', foo='1')
>>> parser.parse_args([])
Namespace()
conflict_handler (str, optional): Defaults to "error".
The strategy for resolving conflicting optionals (usually unnecessary).

ArgumentParser objects do not allow two actions with the same option string. By default, ArgumentParser objects raise an exception if an attempt is made to create an argument with an option string that is already in use:
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('-f', '--foo', help='old foo help')
>>> parser.add_argument('--foo', help='new foo help')
Traceback (most recent call last):
..
ArgumentError: argument --foo: conflicting option string(s): --foo
Sometimes (e.g. when using parents) it may be useful to simply override any older arguments with the same option string. To get this behavior, the value 'resolve' can be supplied to the conflict_handler= argument of ArgumentParser:
>>> parser = argparse.ArgumentParser(prog='PROG', conflict_handler='resolve')
>>> parser.add_argument('-f', '--foo', help='old foo help')
>>> parser.add_argument('--foo', help='new foo help')
>>> parser.print_help()
usage: PROG [-h] [-f FOO] [--foo FOO]

options:
  -h, --help  show this help message and exit -f FOO      old foo help --foo FOO   new foo help
Note that ArgumentParser objects only remove an action if all of its option strings are overridden. So, in the example above, the old -f/--foo action is retained as the -f action, because only the --foo option string was overridden.
add_help (bool, optional): Defaults to True.
Add a -h/--help option to the parser (default: True).

By default, ArgumentParser objects add an option which simply displays the parser’s help message. For example, consider a file named myprogram.py containing the following code:
import argparse parser = argparse.ArgumentParser()
parser.add_argument('--foo', help='foo help')
args = parser.parse_args()
If -h or --help is supplied at the command line, the ArgumentParser help will be printed:
$ python myprogram.py --help
usage: myprogram.py [-h] [--foo FOO]

options:
  -h, --help  show this help message and exit
  --foo FOO   foo help
Occasionally, it may be useful to disable the addition of this help option. This can be achieved by passing False as the add_help= argument to ArgumentParser:
>>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
>>> parser.add_argument('--foo', help='foo help')
>>> parser.print_help()
usage: PROG [--foo FOO]

options: --foo FOO  foo help
The help option is typically -h/--help. The exception to this is if the prefix_chars= is specified and does not include -, in which case -h and --help are not valid options. In this case, the first character in prefix_chars is used to prefix the help options:
>>> parser = argparse.ArgumentParser(prog='PROG', prefix_chars='+/')
>>> parser.print_help()
usage: PROG [+h]

options: +h, ++help  show this help message and exit
allow_abbrev (bool, optional): Defaults to True.
Normally, when you pass an argument list to the parse_args() method of an ArgumentParser, it recognizes abbreviations of long options.

This feature can be disabled by setting allow_abbrev to False:
>>> parser = argparse.ArgumentParser(prog='PROG', allow_abbrev=False)
>>> parser.add_argument('--foobar', action='store_true')
>>> parser.add_argument('--foonley', action='store_false')
>>> parser.parse_args(['--foon'])
usage: PROG [-h] [--foobar] [--foonley]
PROG: error: unrecognized arguments: --foon
New in version 3.5.
exit_on_error (bool, optional): Defaults to True.
Normally, when you pass an invalid argument list to the parse_args() method of an ArgumentParser, it will exit with error info.

If the user would like to catch errors manually, the feature can be enabled by setting exit_on_error to False:
>>> parser = argparse.ArgumentParser(exit_on_error=False)
>>> parser.add_argument('--integers', type=int)
_StoreAction(option_strings=['--integers'], dest='integers', nargs=None, const=None, default=None, type=<class 'int'>, choices=None, help=None, metavar=None)
>>> try:
...     parser.parse_args('--integers a'.split())
... except argparse.ArgumentError:
...     print('Catching an argumentError')
...
Catching an argumentError
New in version 3.9.

Returns

Callable[[type[Class]], type[Class]]: The decorator used to wrap around dataclass() decorator passing parameters to the ArgumentParser constructor. When it is used with no parameters, just returns the class decorated with dataclass().

dataparsers.parse( cls: type[Class], args: Sequence[str] | None = None, *, parser: ArgumentParser | None = None, ) → Class[source]

Parse command line arguments according to the fields of cls and populate it.

Accepts classes decorated with dataclass().

Parameters

cls (type[Class]):

A dataclass() used as object to take the attributes to parse the command-line arguments.

args (Sequence[str] | None, optional): Defaults to None.

List of strings to parse. The default is taken from sys.argv, like the original parse_args() method.

parser (ArgumentParser | None, optional): Defaults to None.

Existing parser to add arguments to and parse from.

Returns

Class: The populated dataclass() with argument values.

dataparsers.parse_known( cls: type[Class], args: Sequence[str] | None = None, *, parser: ArgumentParser | None = None, metavar: str | None = None, ) → tuple[Class, list[str]][source]

Parse command line arguments according to the fields of cls and populate it.

Same as parse() except that it it does not produce an error when extra arguments are present. Instead, it returns a two item tuple containing the populated class and the list of remaining argument strings.

Accepts classes decorated with dataclass().

Parameters

cls (type[Class]):

A dataclass() used as object to take the attributes to parse the command-line arguments.

args (Sequence[str] | None, optional): Defaults to None.

List of strings to parse. The default is taken from sys.argv, like the original parse_known_args() method.

parser (ArgumentParser | None, optional): Defaults to None.

Existing parser to add arguments to and parse from.

metavar (str | None, optional): Defaults to None.

A name to represent extra remaining arguments that could be present in command line, in the usage message. By default None and no name is printed.

Returns

tuple[Class, list[str]]: A two item tuple containing the populated class and the list of remaining argument strings.

dataparsers.make_parser( cls: type, *, parser: ArgumentParser | None = None, ) → ArgumentParser[source]

Creates a ArgumentParser with command-line arguments according to the fields of cls.

Use this to create a ArgumentParser and not immediately parse the arguments (i.e., save it for later). If you do want to parse immediately, use parse().

Parameters

cls (type):

A dataclass() according to which argument parser is created.

parser (ArgumentParser | None, optional): Defaults to None.

Existing parser to add arguments to. By default creates a new parser.

Returns

ArgumentParser: The new ArgumentParser object or the existing parser with added arguments.

dataparsers.subparser( *, defaults: dict[str, Any] | None = None, aliases: Sequence[str] = Ellipsis, help: str = Ellipsis, prog: str | None = None, usage: str | None = None, description: str | None = None, epilog: str | None = None, parents: Sequence[ArgumentParser] = [], formatter_class: HelpFormatter = Ellipsis, prefix_chars: str = '-', fromfile_prefix_chars: str | None = None, argument_default: Any | None = None, conflict_handler: str = 'error', add_help: bool = True, allow_abbrev: bool = True, exit_on_error: bool = True, ) → Any[source]

Helper function to create dataclass() class variables (ClassVar) storing specification about a subparser, used later in the method add_parser() to add sub commands.

This function accepts all the parameters of the original add_parser() method and an additional parameter named defaults, which receives a dictionary with the subparser-level defaults attributes that are determined without any inspection of the command line.

Parameters

defaults (dict[str, Any] | None = None, optional): Defaults to None.

A dictionary that allows some additional attributes of the subparser to be determined without any inspection of the command line.

The dictionary keys must be defined previously with the default() function.

Extra parameters of the original `add_parser()` method

aliases (Sequence[str], optional):

An additional argument which allows multiple strings to refer to the same subparser. This example, like svn, aliases co as a shorthand for checkout:
>>> parser = argparse.ArgumentParser()
>>> subparsers = parser.add_subparsers()
>>> checkout = subparsers.add_parser('checkout', aliases=['co'])
>>> checkout.add_argument('foo')
>>> parser.parse_args(['co', 'bar'])
Namespace(foo='bar')

help (str, optional):

A help message for each subparser command can be given by supplying this argument o add_parser() as below:

>>> # create the top-level parser
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('--foo', action='store_true', help='foo help')
>>> subparsers = parser.add_subparsers(help='sub-command help')
>>>
>>> # create the parser for the "a" command
>>> parser_a = subparsers.add_parser('a', help='a help')
>>> parser_a.add_argument('bar', type=int, help='bar help')
>>>
>>> # create the parser for the "b" command
>>> parser_b = subparsers.add_parser('b', help='b help')
>>> parser_b.add_argument('--baz', choices='XYZ', help='baz help')
>>> parser.parse_args(['--help'])
usage: PROG [-h] [--foo] {a,b} ...

positional arguments:
  {a,b}   sub-command help
    a     a help
    b     b help

options:
  -h, --help  show this help message and exit
  --foo   foo help

Parameters from the original `ArgumentParser` constructor

See the dataparser() decorator parameters.

Returns

Field: A dataclass() field with a default values assigned as a instance of a read-only SubParser class storing information about the subparser, which must be assigned to a ClassVar field.

dataparsers.subparsers( *, title: str = 'subcommands', description: str | None = None, prog: str = Ellipsis, parser_class: type = <class 'argparse.ArgumentParser'>, action: type[~argparse.Action] = Ellipsis, dest: str | None = None, required: bool = False, help: str | None = None, metavar: str | None = None, ) → str[source]

Helper function to create a dataclass() field storing specification about a subparser group, used later in the method add_subparsers(). This function accepts all parameters of the original add_subparsers() method (except for dest).

Parameters

title (str, optional): Defaults to "subcommands".

Title for the sub-parser group in help output; by default “subcommands” if description is provided, otherwise uses title for positional arguments

description (str | None, optional): Defaults to None.

Description for the sub-parser group in help output.

prog (str, optional): Defaults to the name of the program and any positional arguments before the subparser argument.

Usage information that will be displayed with sub-command help.

parser_class (type, optional): Defaults to ArgumentParser.

Class which will be used to create sub-parser instances, by default the class of the current parser (e.g. ArgumentParser).

action (type[Action], optional): Defaults to ....

The basic type of action to be taken when this argument is encountered at the command line.

dest (str | None, optional): Defaults to None.

Note:
The parameter dest is described here just for documentation. It will raise an error if it is passed to the subparsers() function, because it is not necessary: the dest keyword argument of the add_subparsers() method is taken from the dataclass field name.

Name of the attribute under which sub-command name will be stored. By default None and no value is stored.

required (bool, optional): Defaults to False.

Whether or not a subcommand must be provided (added in 3.7).

help (str | None, optional): Defaults to None.

Help for sub-parser group in help output.

metavar (str | None, optional): Defaults to None.

String presenting available sub-commands in help. By default it is None and presents sub-commands in form {cmd1, cmd2, ..}

Returns

Field[str]: A dataclass() field with metadata dictionary filled with subparser group parameters.

dataparsers.write_help( text: str, width: int | None = None, space: int = 24, dedent: bool = True, final_newlines: bool = True, ) → str[source]

Writes formatted help text (wrapped) preserving ‘new lines’. This is supplied as an option to use in the help_formatter argument.

Parameters

text (str):

The help text.

width (int, optional): Defaults to None.

The width of the help text to wrap (if None, use terminal COLUMNS).

space (int, optional): Defaults to 24.

The indentation space used in in CLI helps.

dedent (bool, optional): Defaults to True.

Whether to remove blank spaces at start and end of lines.

final_newlines (bool, optional): Defaults to True.

Whether to add a final empty line.

Returns

str: The help text formatted (wrapped and preserving new lines)

Available functions

Parameters

Parameters from the original add_argument() method

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Parameters from the original ArgumentParser class

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Extra parameters of the original add_parser() method

Parameters from the original ArgumentParser constructor

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Parameters from the original `add_argument()` method

Parameters from the original `ArgumentParser` class

Extra parameters of the original `add_parser()` method

Parameters from the original `ArgumentParser` constructor