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Diffstat (limited to 'Doc/library/argparse.rst')
| -rw-r--r-- | Doc/library/argparse.rst | 405 |
1 files changed, 203 insertions, 202 deletions
diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst index ab095e4..7267ae4 100644 --- a/Doc/library/argparse.rst +++ b/Doc/library/argparse.rst @@ -137,40 +137,136 @@ ArgumentParser objects argument_default=None, conflict_handler='error', \ add_help=True) - Create a new :class:`ArgumentParser` object. Each parameter has its own more - detailed description below, but in short they are: + Create a new :class:`ArgumentParser` object. All parameters should be passed + as keyword arguments. Each parameter has its own more detailed description + below, but in short they are: - * description_ - Text to display before the argument help. + * prog_ - The name of the program (default: ``sys.argv[0]``) - * epilog_ - Text to display after the argument help. + * usage_ - The string describing the program usage (default: generated from + arguments added to parser) - * add_help_ - Add a -h/--help option to the parser. (default: ``True``) + * description_ - Text to display before the argument help (default: none) - * argument_default_ - Set the global default value for arguments. - (default: ``None``) + * epilog_ - Text to display after the argument help (default: none) * parents_ - A list of :class:`ArgumentParser` objects whose arguments should - also be included. + also be included + + * formatter_class_ - A class for customizing the help output - * prefix_chars_ - The set of characters that prefix optional arguments. + * prefix_chars_ - The set of characters that prefix optional arguments (default: '-') * fromfile_prefix_chars_ - The set of characters that prefix files from - which additional arguments should be read. (default: ``None``) - - * formatter_class_ - A class for customizing the help output. + which additional arguments should be read (default: ``None``) - * conflict_handler_ - Usually unnecessary, defines strategy for resolving - conflicting optionals. + * argument_default_ - The global default value for arguments + (default: ``None``) - * prog_ - The name of the program (default: - ``sys.argv[0]``) + * conflict_handler_ - The strategy for resolving conflicting optionals + (usually unnecessary) - * usage_ - The string describing the program usage (default: generated) + * add_help_ - Add a -h/--help option to the parser (default: ``True``) The following sections describe how each of these are used. +prog +^^^^ + +By default, :class:`ArgumentParser` objects uses ``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] + + optional arguments: + -h, --help show this help message and exit + --foo FOO foo help + $ cd .. + $ python subdir\myprogram.py --help + usage: myprogram.py [-h] [--foo FOO] + + optional arguments: + -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 :class:`ArgumentParser`:: + + >>> parser = argparse.ArgumentParser(prog='myprogram') + >>> parser.print_help() + usage: myprogram [-h] + + optional arguments: + -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] + + optional arguments: + -h, --help show this help message and exit + --foo FOO foo of the myprogram program + + +usage +^^^^^ + +By default, :class:`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 + + optional arguments: + -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 + + optional arguments: + -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 ^^^^^^^^^^^ @@ -218,122 +314,6 @@ line-wrapped, but this behavior can be adjusted with the formatter_class_ argument to :class:`ArgumentParser`. -add_help -^^^^^^^^ - -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] - - optional arguments: - -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 -:class:`ArgumentParser`:: - - >>> parser = argparse.ArgumentParser(prog='PROG', add_help=False) - >>> parser.add_argument('--foo', help='foo help') - >>> parser.print_help() - usage: PROG [--foo FOO] - - optional arguments: - --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] - - optional arguments: - +h, ++help show this help message and exit - - -prefix_chars -^^^^^^^^^^^^ - -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 -^^^^^^^^^^^^^^^^^^^^^ - -Sometimes, for example when dealing with a particularly long argument lists, 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 -:class:`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') 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 -:meth:`~ArgumentParser.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']``. - -The ``fromfile_prefix_chars=`` argument defaults to ``None``, meaning that -arguments will never be treated as file references. - - -argument_default -^^^^^^^^^^^^^^^^ - -Generally, argument defaults are specified either by passing a default to -:meth:`~ArgumentParser.add_argument` or by calling the -:meth:`~ArgumentParser.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 :class:`ArgumentParser`. For example, -to globally suppress attribute creation on :meth:`~ArgumentParser.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() - - parents ^^^^^^^ @@ -471,6 +451,74 @@ as the regular formatter does):: --foo int +prefix_chars +^^^^^^^^^^^^ + +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 +^^^^^^^^^^^^^^^^^^^^^ + +Sometimes, for example when dealing with a particularly long argument lists, 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 +:class:`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') 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 +:meth:`~ArgumentParser.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']``. + +The ``fromfile_prefix_chars=`` argument defaults to ``None``, meaning that +arguments will never be treated as file references. + + +argument_default +^^^^^^^^^^^^^^^^ + +Generally, argument defaults are specified either by passing a default to +:meth:`~ArgumentParser.add_argument` or by calling the +:meth:`~ArgumentParser.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 :class:`ArgumentParser`. For example, +to globally suppress attribute creation on :meth:`~ArgumentParser.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 ^^^^^^^^^^^^^^^^ @@ -508,22 +556,20 @@ action is retained as the ``-f`` action, because only the ``--foo`` option string was overridden. -prog -^^^^ +add_help +^^^^^^^^ -By default, :class:`ArgumentParser` objects uses ``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:: +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() -The help for this program will display ``myprogram.py`` as the program name -(regardless of where the program was invoked from):: +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] @@ -531,76 +577,31 @@ The help for this program will display ``myprogram.py`` as the program name optional arguments: -h, --help show this help message and exit --foo FOO foo help - $ cd .. - $ python subdir\myprogram.py --help - usage: myprogram.py [-h] [--foo FOO] - optional arguments: - -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 :class:`ArgumentParser`:: - - >>> parser = argparse.ArgumentParser(prog='myprogram') - >>> parser.print_help() - usage: myprogram [-h] - - optional arguments: - -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] - - optional arguments: - -h, --help show this help message and exit - --foo FOO foo of the myprogram program - - -usage -^^^^^ - -By default, :class:`ArgumentParser` calculates the usage message from the -arguments it contains:: +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 +:class:`ArgumentParser`:: - >>> parser = argparse.ArgumentParser(prog='PROG') - >>> parser.add_argument('--foo', nargs='?', help='foo help') - >>> parser.add_argument('bar', nargs='+', help='bar help') + >>> parser = argparse.ArgumentParser(prog='PROG', add_help=False) + >>> parser.add_argument('--foo', help='foo help') >>> parser.print_help() - usage: PROG [-h] [--foo [FOO]] bar [bar ...] - - positional arguments: - bar bar help + usage: PROG [--foo FOO] optional arguments: - -h, --help show this help message and exit - --foo [FOO] foo help + --foo FOO foo help -The default message can be overridden with the ``usage=`` keyword argument:: +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', usage='%(prog)s [options]') - >>> parser.add_argument('--foo', nargs='?', help='foo help') - >>> parser.add_argument('bar', nargs='+', help='bar help') + >>> parser = argparse.ArgumentParser(prog='PROG', prefix_chars='+/') >>> parser.print_help() - usage: PROG [options] - - positional arguments: - bar bar help + usage: PROG [-h] optional arguments: - -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. + -h, --help show this help message and exit The add_argument() method |