[Python-checkins] r78615 - in python/branches/py3k: Doc/library/argparse.rst
benjamin.peterson
python-checkins at python.org
Wed Mar 3 03:07:08 CET 2010
Author: benjamin.peterson
Date: Wed Mar 3 03:07:08 2010
New Revision: 78615
Log:
Merged revisions 78613-78614 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r78613 | benjamin.peterson | 2010-03-02 19:55:09 -0600 (Tue, 02 Mar 2010) | 1 line
edit for style
........
r78614 | benjamin.peterson | 2010-03-02 20:04:24 -0600 (Tue, 02 Mar 2010) | 1 line
fix Sphinx warnings
........
Modified:
python/branches/py3k/ (props changed)
python/branches/py3k/Doc/library/argparse.rst
Modified: python/branches/py3k/Doc/library/argparse.rst
==============================================================================
--- python/branches/py3k/Doc/library/argparse.rst (original)
+++ python/branches/py3k/Doc/library/argparse.rst Wed Mar 3 03:07:08 2010
@@ -9,17 +9,16 @@
The :mod:`argparse` module makes it easy to write user friendly command line
-interfaces. You define what arguments your program requires, and :mod:`argparse`
+interfaces. The program defines what arguments it requires, and :mod:`argparse`
will figure out how to parse those out of :data:`sys.argv`. The :mod:`argparse`
-module also automatically generates help and usage messages based on the
-arguments you have defined, and issues errors when users give your program
-invalid arguments.
+module also automatically generates help and usage messages and issues errors
+when users give the program invalid arguments.
Example
-------
-As an example, the following code is a Python program that takes a list of
-integers and produces either the sum or the max::
+The following code is a Python program that takes a list of integers and
+produces either the sum or the max::
import argparse
@@ -68,24 +67,23 @@
Creating a parser
^^^^^^^^^^^^^^^^^
-Pretty much every script that uses the :mod:`argparse` module will start out by
-creating an :class:`ArgumentParser` object::
+Mose uses of the :mod:`argparse` module will start out by creating an
+:class:`ArgumentParser` object::
>>> parser = argparse.ArgumentParser(description='Process some integers.')
The :class:`ArgumentParser` object will hold all the information necessary to
-parse the command line into a more manageable form for your program.
+parse the command line into python data types.
Adding arguments
^^^^^^^^^^^^^^^^
-Once you've created an :class:`ArgumentParser`, you'll want to fill it with
-information about your program arguments. You typically do this by making calls
-to the :meth:`add_argument` method. Generally, these calls tell the
-:class:`ArgumentParser` how to take the strings on the command line and turn
-them into objects for you. This information is stored and used when
-:meth:`parse_args` is called. For example, if we add some arguments like this::
+Filling an :class:`ArgumentParser` with information about program arguments is
+done by making calls to the :meth:`~ArgumentParser.add_argument` method.
+Generally, these calls tell the :class:`ArgumentParser` how to take the strings
+on the command line and turn them into objects. This information is stored and
+used when :meth:`~ArgumentParser.parse_args` is called. For example::
>>> parser.add_argument('integers', metavar='N', type=int, nargs='+',
... help='an integer for the accumulator')
@@ -93,7 +91,7 @@
... const=sum, default=max,
... help='sum the integers (default: find the max)')
-when we later call :meth:`parse_args`, we can expect it to return an object with
+Later, calling :meth:`parse_args` will return an object with
two attributes, ``integers`` and ``accumulate``. The ``integers`` attribute
will be a list of one or more ints, and the ``accumulate`` attribute will be
either the :func:`sum` function, if ``--sum`` was specified at the command line,
@@ -102,9 +100,8 @@
Parsing arguments
^^^^^^^^^^^^^^^^^
-Once an :class:`ArgumentParser` has been initialized with appropriate calls to
-:meth:`add_argument`, it can be instructed to parse the command-line args by
-calling the :meth:`parse_args` method. This will inspect the command-line,
+:class:`ArgumentParser` parses args through the
+:meth:`~ArgumentParser.parse_args` method. This will inspect the command-line,
convert each arg to the appropriate type and then invoke the appropriate action.
In most cases, this means a simple namespace object will be built up from
attributes parsed out of the command-line::
@@ -112,10 +109,9 @@
>>> parser.parse_args(['--sum', '7', '-1', '42'])
Namespace(accumulate=<built-in function sum>, integers=[7, -1, 42])
-In a script, :meth:`parse_args` will typically be called with no arguments, and
-the :class:`ArgumentParser` will automatically determine the command-line args
-from :data:`sys.argv`. That's pretty much it. You're now ready to go write
-some command line interfaces!
+In a script, :meth:`~ArgumentParser.parse_args` will typically be called with no
+arguments, and the :class:`ArgumentParser` will automatically determine the
+command-line args from :data:`sys.argv`.
ArgumentParser objects
@@ -130,41 +126,41 @@
* epilog_ - Text to display after the argument help.
- * add_help_ - Add a -h/--help option to the parser. (default: True)
+ * add_help_ - Add a -h/--help option to the parser. (default: ``True``)
* argument_default_ - Set the global default value for arguments.
- (default: None)
+ (default: ``None``)
- * parents_ - A list of :class:ArgumentParser objects whose arguments should
+ * parents_ - A list of :class:`ArgumentParser` objects whose arguments should
also be included.
* 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)
+ which additional arguments should be read. (default: ``None``)
* formatter_class_ - A class for customizing the help output.
* conflict_handler_ - Usually unnecessary, defines strategy for resolving
conflicting optionals.
- * prog_ - Usually unnecessary, the name of the program
- (default: ``sys.argv[0]``)
+ * prog_ - The name of the program (default:
+ :data:`sys.argv[0]`)
- * usage_ - Usually unnecessary, the string describing the program usage
- (default: generated)
+ * usage_ - The string describing the program usage (default: generated)
- The following sections describe how each of these are used.
+The following sections describe how each of these are used.
description
^^^^^^^^^^^
-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::
+Most calls to the :class:`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()
@@ -201,7 +197,7 @@
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.
+argument to :class:`ArgumentParser`.
add_help
@@ -228,7 +224,7 @@
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::
+:class:`ArgumentParser`::
>>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
>>> parser.add_argument('--foo', help='foo help')
@@ -261,14 +257,15 @@
fromfile_prefix_chars
^^^^^^^^^^^^^^^^^^^^^
-Sometimes, e.g. for 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 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::
+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::
- >>> open('args.txt', 'w').write('-f\nbar')
+ >>> 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'])
@@ -290,9 +287,9 @@
:meth:`add_argument` or by calling the :meth:`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 :meth:`parse_args` calls, we
-supply ``argument_default=SUPPRESS``::
+passing the ``argument_default=`` keyword argument to :class:`ArgumentParser`.
+For example, to globally suppress attribute creation on :meth:`parse_args`
+calls, we supply ``argument_default=SUPPRESS``::
>>> parser = argparse.ArgumentParser(argument_default=argparse.SUPPRESS)
>>> parser.add_argument('--foo')
@@ -307,12 +304,11 @@
^^^^^^^
Sometimes, several parsers share a common set of arguments. Rather than
-repeating the definitions of these arguments, you can define a single parser
-with all the shared arguments and then use the ``parents=`` argument to
-ArgumentParser to have these "inherited". 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::
+repeating the definitions of these arguments, a single parser with all the
+shared arguments and passed to ``parents=`` argument to :class:`ArgumentParser`
+can be used. The ``parents=`` argument takes a list of :class:`ArgumentParser`
+objects, collects all the positional and optional actions from them, and adds
+these actions to the :class:`ArgumentParser` object being constructed::
>>> parent_parser = argparse.ArgumentParser(add_help=False)
>>> parent_parser.add_argument('--parent', type=int)
@@ -328,23 +324,23 @@
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.
+:class:`ArgumentParser` will see two ``-h/--help`` options (one in the parent
+and one in the child) and raise an error.
formatter_class
^^^^^^^^^^^^^^^
-ArgumentParser objects allow the help formatting to be customized by specifying
-an alternate formatting class. Currently, there are three such classes:
-:class:`argparse.RawDescriptionHelpFormatter`,
+:class:`ArgumentParser` objects allow the help formatting to be customized by
+specifying an alternate formatting class. Currently, there are three such
+classes: :class:`argparse.RawDescriptionHelpFormatter`,
:class:`argparse.RawTextHelpFormatter` and
:class:`argparse.ArgumentDefaultsHelpFormatter`. The first two allow more
control over how textual descriptions are displayed, while the last
automatically adds information about argument default values.
-By default, ArgumentParser objects line-wrap the description_ and epilog_ texts
-in command-line help messages::
+By default, :class:`ArgumentParser` objects line-wrap the description_ and
+epilog_ texts in command-line help messages::
>>> parser = argparse.ArgumentParser(
... prog='PROG',
@@ -366,10 +362,9 @@
likewise for this epilog whose whitespace will be cleaned up and whose words
will be wrapped across a couple lines
-When you have description_ and epilog_ that is already correctly formatted and
-should not be line-wrapped, you can indicate this by passing
-``argparse.RawDescriptionHelpFormatter`` as the ``formatter_class=`` argument to
-ArgumentParser::
+Passing :class:`argparse.RawDescriptionHelpFormatter` as ``formatter_class=``
+indicates that description_ and epilog_ are already correctly formatted and
+should not be line-wrapped::
>>> parser = argparse.ArgumentParser(
... prog='PROG',
@@ -393,10 +388,10 @@
optional arguments:
-h, --help show this help message and exit
-If you want to maintain whitespace for all sorts of help text (including
-argument descriptions), you can use ``argparse.RawTextHelpFormatter``.
+:class:`RawTextHelpFormatter` maintains whitespace for all sorts of help text
+including argument descriptions.
-The other formatter class available, ``argparse.ArgumentDefaultsHelpFormatter``,
+The other formatter class available, :class:`ArgumentDefaultsHelpFormatter`,
will add information about the default value of each of the arguments::
>>> parser = argparse.ArgumentParser(
@@ -418,9 +413,10 @@
conflict_handler
^^^^^^^^^^^^^^^^
-ArgumentParser objects do not allow two actions with the same option string. By
-default, ArgumentParser objects will raise an exception if you try to create an
-argument with an option string that is already in use::
+:class:`ArgumentParser` objects do not allow two actions with the same option
+string. By default, :class:`ArgumentParser` objects raises 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')
@@ -432,7 +428,7 @@
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::
+:class:`ArgumentParser`::
>>> parser = argparse.ArgumentParser(prog='PROG', conflict_handler='resolve')
>>> parser.add_argument('-f', '--foo', help='old foo help')
@@ -445,20 +441,20 @@
-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.
+Note that :class:`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.
prog
^^^^
-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
-what you want because it will make the help messages match what your users have
-typed at the command line. For example, consider a file named ``myprogram.py``
-with the following code::
+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 pgoram was
+invoked on the command line. For example, consider a file named
+``myprogram.py`` with the following code::
import argparse
parser = argparse.ArgumentParser()
@@ -483,7 +479,7 @@
--foo FOO foo help
To change this default behavior, another value can be supplied using the
-``prog=`` argument to ArgumentParser::
+``prog=`` argument to :class:`ArgumentParser`::
>>> parser = argparse.ArgumentParser(prog='myprogram')
>>> parser.print_help()
@@ -511,7 +507,7 @@
usage
^^^^^
-By default, ArgumentParser objects calculate the usage message from the
+By default, :class:`ArgumentParser` calculates the usage message from the
arguments it contains::
>>> parser = argparse.ArgumentParser(prog='PROG')
@@ -527,9 +523,7 @@
-h, --help show this help message and exit
--foo [FOO] foo help
-If the default usage message is not appropriate for your application, you can
-supply your own usage message using the ``usage=`` keyword argument to
-ArgumentParser::
+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')
@@ -544,14 +538,14 @@
-h, --help show this help message and exit
--foo [FOO] foo help
-Note you can use the ``%(prog)s`` format specifier to fill in the program name
-in your usage messages.
+The ``%(prog)s`` format specifier is available to fill in the program name in
+your usage messages.
The add_argument() method
-------------------------
-.. method:: add_argument(name or flags..., [action], [nargs], [const], [default], [type], [choices], [required], [help], [metavar], [dest])
+.. method:: ArgumentParser.add_argument(name or flags..., [action], [nargs], [const], [default], [type], [choices], [required], [help], [metavar], [dest])
Define how a single command line argument should be parsed. Each parameter
has its own more detailed description below, but in short they are:
@@ -583,16 +577,16 @@
* dest_ - The name of the attribute to be added to the object returned by
:meth:`parse_args`.
- The following sections describe how each of these are used.
+The following sections describe how each of these are used.
name or flags
^^^^^^^^^^^^^
-The :meth:`add_argument` method needs to know whether you're expecting an
-optional argument, e.g. ``-f`` or ``--foo``, or a positional argument, e.g. a
-list of filenames. The first arguments passed to :meth:`add_argument` must
-therefore be either a series of flags, or a simple argument name. For example,
-an optional argument could be created like::
+The :meth:`add_argument` method must know whether an optional argument, like
+``-f`` or ``--foo``, or a positional argument, like a list of filenames, is
+expected. The first arguments passed to :meth:`add_argument` must therefore be
+either a series of flags, or a simple argument name. For example, an optional
+argument could be created like::
>>> parser.add_argument('-f', '--foo')
@@ -620,10 +614,8 @@
:class:`ArgumentParser` objects associate command-line args with actions. These
actions can do just about anything with the command-line args associated with
them, though most actions simply add an attribute to the object returned by
-:meth:`parse_args`. When you specify a new argument using the
-:meth:`add_argument` method, you can indicate how the command-line args should
-be handled by specifying the ``action`` keyword argument. The supported actions
-are:
+:meth:`parse_args`. The ``action`` keyword argument specifies how the
+command-line args should be handled. The supported actions are:
* ``'store'`` - This just stores the argument's value. This is the default
action. For example::
@@ -634,10 +626,9 @@
Namespace(foo='1')
* ``'store_const'`` - This stores the value specified by the const_ keyword
- argument. Note that the const_ keyword argument defaults to ``None``, so
- you'll almost always need to provide a value for it. The ``'store_const'``
- action is most commonly used with optional arguments that specify some sort
- of flag. For example::
+ argument. (Note that the const_ keyword argument defaults to the rather
+ unhelpful ``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)
@@ -645,8 +636,8 @@
Namespace(foo=42)
* ``'store_true'`` and ``'store_false'`` - These store the values ``True`` and
- ``False`` respectively. These are basically special cases of
- ``'store_const'``. For example::
+ ``False`` respectively. These are special cases of ``'store_const'``. For
+ example::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='store_true')
@@ -655,8 +646,8 @@
Namespace(bar=False, foo=True)
* ``'append'`` - This stores a list, and appends each argument value to the
- list. This is useful when you want to allow an option to be specified
- multiple times. Example usage::
+ list. This is useful to allow an option to be specified multiple times.
+ Example usage::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='append')
@@ -664,10 +655,10 @@
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``, so you'll almost always need to provide a value
- for it. The ``'append_const'`` action is typically useful when you want
- multiple arguments to store constants to the same list, for example::
+ 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)
@@ -686,9 +677,9 @@
PROG 2.0
You can also specify an arbitrary action by passing an object that implements
-the Action API. The easiest way to do this is to extend ``argparse.Action``,
-supplying an appropriate :meth:`__call__` method. The ``__call__`` method
-accepts four parameters:
+the Action API. The easiest way to do this is to extend
+:class:`argparse.Action`, supplying an appropriate ``__call__`` method. The
+``__call__`` method should accept four parameters:
* ``parser`` - The ArgumentParser object which contains this action.
@@ -703,7 +694,7 @@
The ``option_string`` argument is optional, and will be absent if the action
is associated with a positional argument.
-So for example::
+An example of a custom action::
>>> class FooAction(argparse.Action):
... def __call__(self, parser, namespace, values, option_string=None):
@@ -724,9 +715,9 @@
^^^^^
ArgumentParser objects usually associate a single command-line argument with a
-single action to be taken. In the situations where you'd like to associate a
-different number of command-line arguments with a single action, you can use the
-``nargs`` keyword argument to :meth:`add_argument`. The supported values are:
+single action to be taken. The ``nargs`` keyword argument associates a
+different number of command-line arguments with a single action.. The supported
+values are:
* N (an integer). N args from the command-line will be gathered together into a
list. For example::
@@ -846,8 +837,8 @@
Namespace(foo=42)
-If you don't want to see an attribute when an option was not present at the
-command line, you can supply ``default=argparse.SUPPRESS``::
+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)
@@ -862,10 +853,10 @@
By default, ArgumentParser objects read command-line args in as simple strings.
However, quite often the command-line string should instead be interpreted as
-another type, e.g. :class:`float`, :class:`int` or :class:`file`. The ``type``
-keyword argument of :meth:`add_argument` allows any necessary type-checking and
-type-conversions to be performed. Many common builtin types can be used
-directly as the value of the ``type`` argument::
+another type, like a :class:`float`, :class:`int` or :class:`file`. The
+``type`` keyword argument of :meth:`add_argument` allows any necessary
+type-checking and type-conversions to be performed. Many common builtin types
+can be used directly as the value of the ``type`` argument::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('foo', type=int)
@@ -883,9 +874,8 @@
>>> parser.parse_args(['out.txt'])
Namespace(bar=<open file 'out.txt', mode 'w' at 0x...>)
-If you need to do some special type-checking or type-conversions, you can
-provide your own types by passing to ``type=`` a callable that takes a single
-string argument and returns the type-converted value::
+``type=`` can take any callable that takes a single string argument and returns
+the type-converted value::
>>> def perfect_square(string):
... value = int(string)
@@ -903,8 +893,8 @@
usage: PROG [-h] foo
PROG: error: argument foo: '7' is not a perfect square
-Note that if your type-checking function is just checking for a particular set
-of values, it may be more convenient to use the choices_ keyword argument::
+The choices_ keyword argument may be more convenient for type checkers that
+simply check against a range of values::
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('foo', type=int, choices=xrange(5, 10))
@@ -921,11 +911,10 @@
^^^^^^^
Some command-line args should be selected from a restricted set of values.
-ArgumentParser objects can be told about such sets of values by passing a
-container object as the ``choices`` keyword argument to :meth:`add_argument`.
-When the command-line is parsed with :meth:`parse_args`, arg values will be
-checked, and an error message will be displayed if the arg was not one of the
-acceptable values::
+These can be handled by passing a container object as the ``choices`` keyword
+argument to :meth:`add_argument`. When the command-line is parsed, arg values
+will be checked, and an error message will be displayed if the arg was not one
+of the acceptable values::
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('foo', choices='abc')
@@ -957,9 +946,8 @@
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 change this behavior, i.e. to make an option *required*, the value ``True``
-should be specified for the ``required=`` keyword argument to
-:meth:`add_argument`::
+To make an option *required*, ``True`` can be specified for the ``required=``
+keyword argument to :meth:`add_argument`::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', required=True)
@@ -972,20 +960,18 @@
As the example shows, if an option is marked as ``required``, :meth:`parse_args`
will report an error if that option is not present at the command line.
-**Warning:** Required options are generally considered bad form - normal users
-expect *options* to be *optional*. You should avoid the use of required options
-whenever possible.
+.. note::
+
+ Required options are generally considered bad form because users expect
+ *options* to be *optional*, and thus they should be avoided when possible.
help
^^^^
-A great command-line interface isn't worth anything if your users can't figure
-out which option does what. So for the end-users, ``help`` is probably the most
-important argument to include in your :meth:`add_argument` calls. The ``help``
-value should be a string containing a brief description of what the argument
-specifies. When a user requests help (usually by using ``-h`` or ``--help`` at
-the command-line), these ``help`` descriptions will be displayed with each
+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')
@@ -1024,15 +1010,14 @@
metavar
^^^^^^^
-When ArgumentParser objects generate help messages, they need some way to refer
+When :class:`ArgumentParser` generates help messages, it need 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 if we have a single positional argument with
-``dest='bar'``, that argument will be referred to as ``bar``. And if we have a
-single optional argument ``--foo`` that should be followed by a single
-command-line arg, that arg will be referred to as ``FOO``. You can see this
-behavior in the example below::
+the dest_ value is uppercased. So, a single positional argument with
+``dest='bar'`` will that argument will be referred to as ``bar``. A single
+optional argument ``--foo`` that should be followed by a single command-line arg
+will be referred to as ``FOO``. An example::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo')
@@ -1049,9 +1034,7 @@
-h, --help show this help message and exit
--foo FOO
-If you would like to provide a different name for your argument in help
-messages, you can supply a value for the ``metavar`` keyword argument to
-:meth:`add_argument`::
+An alternative name can be specified with ``metavar``::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', metavar='YYY')
@@ -1073,8 +1056,8 @@
value.
Different values of ``nargs`` may cause the metavar to be used multiple times.
-If you'd like to specify a different display name for each of the arguments, you
-can provide a tuple to ``metavar``::
+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)
@@ -1091,10 +1074,10 @@
dest
^^^^
-Most ArgumentParser actions add some value as an attribute of the object
-returned by :meth:`parse_args`. The name of this attribute is determined by the
-``dest`` keyword argument of :meth:`add_argument`. For positional argument
-actions, ``dest`` is normally supplied as the first argument to
+Most :class:`ArgumentParser` actions add some value as an attribute of the
+object returned by :meth:`parse_args`. The name of this attribute is determined
+by the ``dest`` keyword argument of :meth:`add_argument`. For positional
+argument actions, ``dest`` is normally supplied as the first argument to
:meth:`add_argument`::
>>> parser = argparse.ArgumentParser()
@@ -1103,7 +1086,7 @@
Namespace(bar='XXX')
For optional argument actions, the value of ``dest`` is normally inferred from
-the option strings. ArgumentParser objects generate the value of ``dest`` by
+the option strings. :class:`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
@@ -1119,9 +1102,7 @@
>>> parser.parse_args('--foo 1 -y 2'.split())
Namespace(foo_bar='1', x='2')
-If you would like to use a different attribute name from the one automatically
-inferred by the ArgumentParser, you can supply it with an explicit ``dest``
-parameter::
+``dest`` allows a custom attribute name to be provided::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', dest='bar')
@@ -1132,9 +1113,9 @@
The parse_args() method
-----------------------
-.. method:: parse_args([args], [namespace])
+.. method:: ArgumentParser.parse_args([args], [namespace])
- Convert the strings to objects and assign them as attributes of the
+ Convert argument strings to objects and assign them as attributes of the
namespace. Return the populated namespace.
Previous calls to :meth:`add_argument` determine exactly what objects are
@@ -1142,7 +1123,7 @@
:meth:`add_argument` for details.
By default, the arg strings are taken from :data:`sys.argv`, and a new empty
- ``Namespace`` object is created for the attributes.
+ :class:`Namespace` object is created for the attributes.
Option value syntax
^^^^^^^^^^^^^^^^^^^
@@ -1159,21 +1140,21 @@
>>> parser.parse_args('--foo FOO'.split())
Namespace(foo='FOO', x=None)
-For long options (options with names longer than a single character), you may
-also pass the option and value as a single command line argument, using ``=`` to
+For long options (options with names longer than a single character), the option
+and value can also be passed as a single command line argument, using ``=`` to
separate them::
>>> parser.parse_args('--foo=FOO'.split())
Namespace(foo='FOO', x=None)
-For short options (options only one character long), you may simply concatenate
-the option and its value::
+For short options (options only one character long), the option and its value
+can be concatenated::
>>> parser.parse_args('-xX'.split())
Namespace(foo=None, x='X')
-You can also combine several short options together, using only a single ``-``
-prefix, as long as only the last option (or none of them) requires a value::
+Several short options can be joined together, using only a single ``-`` prefix,
+as long as only the last option (or none of them) requires a value::
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('-x', action='store_true')
@@ -1263,7 +1244,7 @@
Argument abbreviations
^^^^^^^^^^^^^^^^^^^^^^
-The :meth:`parse_args` method allows you to abbreviate long options if the
+The :meth:`parse_args` method allows long options to be abbreviated if the
abbreviation is unambiguous::
>>> parser = argparse.ArgumentParser(prog='PROG')
@@ -1277,8 +1258,7 @@
usage: PROG [-h] [-bacon BACON] [-badger BADGER]
PROG: error: ambiguous option: -ba could match -badger, -bacon
-As you can see above, you will get an error if you pick a prefix that could
-refer to more than one option.
+An error is produced for arguments that could produce more than one options.
Beyond ``sys.argv``
@@ -1286,9 +1266,7 @@
Sometimes it may be useful to have an ArgumentParser parse args other than those
of :data:`sys.argv`. This can be accomplished by passing a list of strings to
-``parse_args``. You may have noticed that the examples in the argparse
-documentation have made heavy use of this calling style - it is much easier to
-use at the interactive prompt::
+``parse_args``. This is useful for testing at the interactive prompt::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument(
@@ -1306,9 +1284,10 @@
Custom namespaces
^^^^^^^^^^^^^^^^^
-It may also be useful to have an ArgumentParser assign attributes to an already
-existing object, rather than the newly-created Namespace object that is normally
-used. This can be achieved by specifying the ``namespace=`` keyword argument::
+It may also be useful to have an :class:`ArgumentParser` assign attributes to an
+already existing object, rather than the newly-created :class:`Namespace` object
+that is normally used. This can be achieved by specifying the ``namespace=``
+keyword argument::
>>> class C(object):
... pass
@@ -1327,19 +1306,19 @@
Sub-commands
^^^^^^^^^^^^
-.. method:: add_subparsers()
+.. method:: ArgumentParser.add_subparsers()
- A lot of programs split up their functionality into a number of sub-commands,
+ Many programs split up their functionality into a number of sub-commands,
for example, the ``svn`` program can invoke sub-commands like ``svn
- checkout``, ``svn update``, ``svn commit``, etc. Splitting up functionality
+ checkout``, ``svn update``, and ``svn commit``. Splitting up functionality
this way can be a particularly good idea when a program performs several
different functions which require different kinds of command-line arguments.
- ArgumentParser objects support the creation of such sub-commands with the
+ :class:`ArgumentParser` supports the creation of such sub-commands with the
:meth:`add_subparsers` method. The :meth:`add_subparsers` method is normally
called with no arguments and returns an special action object. This object
has a single method, ``add_parser``, which takes a command name and any
- ArgumentParser constructor arguments, and returns an ArgumentParser object
- that can be modified as usual.
+ :class:`ArgumentParser` constructor arguments, and returns an
+ :class:`ArgumentParser` object that can be modified as usual.
Some example usage::
@@ -1371,9 +1350,9 @@
Similarly, when a help message is requested from a subparser, only the help
for that particular parser will be printed. The help message will not
- include parent parser or sibling parser messages. (You can however supply a
- help message for each subparser command by suppling the ``help=`` argument to
- ``add_parser`` as above.)
+ include parent parser or sibling parser messages. (A help message for each
+ subparser command, however, can be given by supplying the ``help=`` argument
+ to ``add_parser`` as above.)
::
@@ -1464,13 +1443,12 @@
>>> args.func(args)
((XYZYX))
- This way, you can let :meth:`parse_args` do all the work for you, and then
- just call the appropriate function after the argument parsing is complete.
- Associating functions with actions like this is typically the easiest way to
- handle the different actions for each of your subparsers. However, if you
- find it necessary to check the name of the subparser that was invoked, you
- can always provide a ``dest`` keyword argument to the :meth:`add_subparsers`
- call::
+ This way, you can let :meth:`parse_args` does the job of calling the
+ appropriate function after argument parsing is complete. Associating
+ functions with actions like this is typically the easiest way to handle the
+ different actions for each of your subparsers. However, if it is necessary
+ to check the name of the subparser that was invoked, the ``dest`` keyword
+ argument to the :meth:`add_subparsers` call will work::
>>> parser = argparse.ArgumentParser()
>>> subparsers = parser.add_subparsers(dest='subparser_name')
@@ -1488,9 +1466,9 @@
.. class:: FileType(mode='r', bufsize=None)
The :class:`FileType` factory creates objects that can be passed to the type
- argument of :meth:`add_argument`. Arguments that have :class:`FileType`
- objects as their type will open command-line args as files with the requested
- modes and buffer sizes:
+ argument of :meth:`ArgumentParser.add_argument`. Arguments that have
+ :class:`FileType` objects as their type will open command-line args as files
+ with the requested modes and buffer sizes:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--output', type=argparse.FileType('wb', 0))
@@ -1510,9 +1488,9 @@
Argument groups
^^^^^^^^^^^^^^^
-.. method:: add_argument_group([title], [description])
+.. method:: ArgumentParser.add_argument_group([title], [description])
- By default, ArgumentParser objects group command-line arguments into
+ By default, :class:`ArgumentParser` groups command-line arguments into
"positional arguments" and "optional arguments" when displaying help
messages. When there is a better conceptual grouping of arguments than this
default one, appropriate groups can be created using the
@@ -1530,11 +1508,12 @@
--foo FOO foo help
The :meth:`add_argument_group` method returns an argument group object which
- has an :meth:`add_argument` method just like a regular ArgumentParser
- objects. When an argument is added to the group, the parser treats it just
- like a normal argument, but displays the argument in a separate group for
- help messages. The :meth:`add_argument_group` method accepts ``title`` and
- ``description`` arguments which can be used to customize this display::
+ has an :meth:`~ArgumentParser.add_argument` method just like a regular
+ :class:`ArgumentParser`. When an argument is added to the group, the parser
+ treats it just like a normal argument, but displays the argument in a
+ separate group for help messages. The :meth:`add_argument_group` method
+ accepts ``title`` and ``description`` arguments which can be used to
+ customize this display::
>>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
>>> group1 = parser.add_argument_group('group1', 'group1 description')
@@ -1554,8 +1533,8 @@
--bar BAR bar help
- Note that any arguments not in your user defined groups will end up back in
- the usual "positional arguments" and "optional arguments" sections.
+ Note that any arguments not your user defined groups will end up back in the
+ usual "positional arguments" and "optional arguments" sections.
Mutual exclusion
@@ -1563,10 +1542,7 @@
.. method:: add_mutually_exclusive_group([required=False])
- Sometimes, you need to make sure that only one of a couple different options
- is specified on the command line. You can create groups of such mutually
- exclusive arguments using the :meth:`add_mutually_exclusive_group` method.
- When :func:`parse_args` is called, argparse will make sure that only one of
+ Create a mutually exclusive group. argparse will make sure that only one of
the arguments in the mutually exclusive group was present on the command
line::
@@ -1595,22 +1571,19 @@
PROG: error: one of the arguments --foo --bar is required
Note that currently mutually exclusive argument groups do not support the
- ``title`` and ``description`` arguments of :meth:`add_argument_group`. This
- may change in the future however, so you are *strongly* recommended to
- specify ``required`` as a keyword argument if you use it.
+ ``title`` and ``description`` arguments of :meth:`add_argument_group`.
Parser defaults
^^^^^^^^^^^^^^^
-.. method:: set_defaults(**kwargs)
+.. method:: ArgumentParser.set_defaults(**kwargs)
Most of the time, the attributes of the object returned by :meth:`parse_args`
will be fully determined by inspecting the command-line args and the argument
- actions described in your :meth:`add_argument` calls. However, sometimes it
- may be useful to add some additional attributes that are determined without
- any inspection of the command-line. The :meth:`set_defaults` method allows
- you to do this::
+ actions. :meth:`ArgumentParser.set_defaults` allows some additional
+ attributes that are determined without any inspection of the command-line to
+ be added::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('foo', type=int)
@@ -1618,9 +1591,7 @@
>>> parser.parse_args(['736'])
Namespace(bar=42, baz='badger', foo=736)
- Note that parser-level defaults always override argument-level defaults. So
- if you set a parser-level default for a name that matches an argument, the
- old argument default will no longer be used::
+ Note that parser-level defaults always override argument-level defaults::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', default='bar')
@@ -1628,14 +1599,15 @@
>>> parser.parse_args([])
Namespace(foo='spam')
- Parser-level defaults can be particularly useful when you're working with
- multiple parsers. See the :meth:`add_subparsers` method for an example of
- this type.
+ Parser-level defaults can be particularly useful when working with multiple
+ parsers. See the :meth:`~ArgumentParser.add_subparsers` method for an
+ example of this type.
-.. method:: get_default(dest)
+.. method:: ArgumentParser.get_default(dest)
Get the default value for a namespace attribute, as set by either
- :meth:`add_argument` or by :meth:`set_defaults`::
+ :meth:`~ArgumentParser.add_argument` or by
+ :meth:`~ArgumentParser.set_defaults`::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', default='badger')
@@ -1647,16 +1619,16 @@
^^^^^^^^^^^^^
In most typical applications, :meth:`parse_args` will take care of formatting
-and printing any usage or error messages. However, should you want to format or
-print these on your own, several methods are available:
+and printing any usage or error messages. However, several formatting methods
+are available:
-.. method:: print_usage([file]):
+.. method:: ArgumentParser.print_usage([file]):
Print a brief description of how the :class:`ArgumentParser` should be
invoked on the command line. If ``file`` is not present, ``sys.stderr`` is
assumed.
-.. method:: print_help([file]):
+.. method:: ArgumentParser.print_help([file]):
Print a help message, including the program usage and information about the
arguments registered with the :class:`ArgumentParser`. If ``file`` is not
@@ -1665,12 +1637,12 @@
There are also variants of these methods that simply return a string instead of
printing it:
-.. method:: format_usage():
+.. method:: ArgumentParser.format_usage():
Return a string containing a brief description of how the
:class:`ArgumentParser` should be invoked on the command line.
-.. method:: format_help():
+.. method:: ArgumentParser.format_help():
Return a string containing a help message, including the program usage and
information about the arguments registered with the :class:`ArgumentParser`.
@@ -1680,14 +1652,14 @@
Partial parsing
^^^^^^^^^^^^^^^
-.. method:: parse_known_args([args], [namespace])
+.. method:: ArgumentParser.parse_known_args([args], [namespace])
Sometimes a script may only parse a few of the command line arguments, passing
the remaining arguments on to another script or program. In these cases, the
:meth:`parse_known_args` method can be useful. It works much like
-:meth:`parse_args` except that it does not produce an error when extra arguments
-are present. Instead, it returns a two item tuple containing the populated
-namespace and the list of remaining argument strings.
+:meth:`~ArgumentParser.parse_args` except that it does not produce an error when
+extra arguments are present. Instead, it returns a two item tuple containing
+the populated namespace and the list of remaining argument strings.
::
@@ -1701,13 +1673,12 @@
Customizing file parsing
^^^^^^^^^^^^^^^^^^^^^^^^
-.. method:: convert_arg_line_to_args(arg_line)
+.. method:: ArgumentParser.convert_arg_line_to_args(arg_line)
Arguments that are read from a file (see the ``fromfile_prefix_chars``
keyword argument to the :class:`ArgumentParser` constructor) are read one
- argument per line. If you need fancier parsing, then you can subclass the
- :class:`ArgumentParser` and override the :meth:`convert_arg_line_to_args`
- method.
+ argument per line. :meth:`convert_arg_line_to_args` can be overriden for
+ fancier reading.
This method takes a single argument ``arg_line`` which is a string read from
the argument file. It returns a list of arguments parsed from this string.
@@ -1735,10 +1706,10 @@
A partial upgrade path from optparse to argparse:
-* Replace all ``add_option()`` calls with :meth:`add_argument` calls.
+* Replace all ``add_option()`` calls with :meth:`ArgumentParser.add_argument` calls.
* Replace ``options, args = parser.parse_args()`` with ``args =
- parser.parse_args()`` and add additional :meth:`add_argument` calls for the
+ parser.parse_args()`` and add additional :meth:`ArgumentParser.add_argument` calls for the
positional arguments.
* Replace callback actions and the ``callback_*`` keyword arguments with
@@ -1747,8 +1718,9 @@
* Replace string names for ``type`` keyword arguments with the corresponding
type objects (e.g. int, float, complex, etc).
-* Replace ``Values`` with ``Namespace`` and ``OptionError/OptionValueError``
- with ``ArgumentError``.
+* Replace :class:`optparse.Values` with :class:`Namespace` and
+ :exc:`optparse.OptionError` and :exc:`optparse.OptionValueError` with
+ :exc:`ArgumentError`.
* Replace strings with implicit arguments such as ``%default`` or ``%prog`` with
the standard python syntax to use dictionaries to format strings, that is,
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