I have created a script using argparse.
The script needs to take a configuration file name as an option, and user can specify whether they need to proceed totally the script or only simulate it.
The args to be passed: ./script -f config_file -s or ./script -f config_file.
It's ok for the -f config_file part, but It keeps asking me for arguments for the -s which is optionnal and should not be followed by any.
I have tried this:
parser = argparse.ArgumentParser()
parser.add_argument('-f', '--file')
#parser.add_argument('-s', '--simulate', nargs = '0')
args = parser.parse_args()
if args.file:
config_file = args.file
if args.set_in_prod:
simulate = True
else:
pass
With the following errors:
File "/usr/local/lib/python2.6/dist-packages/argparse.py", line 2169, in _get_nargs_pattern
nargs_pattern = '(-*%s-*)' % '-*'.join('A' * nargs)
TypeError: can't multiply sequence by non-int of type 'str'
And same errror with '' instead of 0.
As #Felix Kling suggested use action='store_true':
>>> from argparse import ArgumentParser
>>> p = ArgumentParser()
>>> _ = p.add_argument('-f', '--foo', action='store_true')
>>> args = p.parse_args()
>>> args.foo
False
>>> args = p.parse_args(['-f'])
>>> args.foo
True
To create an option that needs no value, set the action [docs] of it to 'store_const', 'store_true' or 'store_false'.
Example:
parser.add_argument('-s', '--simulate', action='store_true')
Related
I want to have some options in argparse module such as --pm-export however when I try to use it like args.pm-export I get the error that there is not attribute pm. How can I get around this issue? Is it possible to have - in command line options?
As indicated in the argparse docs:
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. Any internal - characters will be converted to _ characters to make sure the string is a valid attribute name
So you should be using args.pm_export.
Unfortunately, dash-to-underscore replacement doesn't work for positional arguments (not prefixed by --).
E.g:
parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument('logs-dir',
help='Directory with .log and .log.gz files')
parser.add_argument('results-csv', type=argparse.FileType('w'),
default=sys.stdout,
help='Output .csv filename')
args = parser.parse_args()
print args
# gives
# Namespace(logs-dir='./', results-csv=<open file 'lool.csv', mode 'w' at 0x9020650>)
So, you should use 1'st argument to add_argument() as attribute name and metavar kwarg to set how it should look in help:
parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument('logs_dir', metavar='logs-dir',
nargs=1,
help='Directory with .log and .log.gz files')
parser.add_argument('results_csv', metavar='results-csv',
nargs=1,
type=argparse.FileType('w'),
default=sys.stdout,
help='Output .csv filename')
args = parser.parse_args()
print args
# gives
# Namespace(logs_dir=['./'], results_csv=[<open file 'lool.csv', mode 'w' at 0xb71385f8>])
Dashes are converted to underscores:
import argparse
pa = argparse.ArgumentParser()
pa.add_argument('--foo-bar')
args = pa.parse_args(['--foo-bar', '24'])
print args # Namespace(foo_bar='24')
Concise and explicit but probably not always acceptable way would be to use vars():
#!/usr/bin/env python3
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('a-b')
args = vars(parser.parse_args())
print(args['a-b'])
getattr(args, 'positional-arg')
This is another OK workaround for positional arguments:
#!/usr/bin/env python3
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('a-b')
args = parser.parse_args(['123'])
assert getattr(args, 'a-b') == '123'
Tested on Python 3.8.2.
I guess the last option is to change shorten option -a to --a
import argparse
parser = argparse.ArgumentParser(description="Help")
parser.add_argument("--a", "--argument-option", metavar="", help="") # change here
args = parser.parse_args()
option = args.a # And here
print(option)
With python's argparse, how do I make a subcommand a required argument? I want to do this because I want argparse to error out if a subcommand is not specified. I override the error method to print help instead. I have 3-deep nested subcommands, so it's not a matter of simply handling zero arguments at the top level.
In the following example, if this is called like so, I get:
$./simple.py
$
What I want it to do instead is for argparse to complain that the required subcommand was not specified:
import argparse
class MyArgumentParser(argparse.ArgumentParser):
def error(self, message):
self.print_help(sys.stderr)
self.exit(0, '%s: error: %s\n' % (self.prog, message))
def main():
parser = MyArgumentParser(description='Simple example')
subs = parser.add_subparsers()
sub_one = subs.add_parser('one', help='does something')
sub_two = subs.add_parser('two', help='does something else')
parser.parse_args()
if __name__ == '__main__':
main()
There was a change in 3.3 in the error message for required arguments, and subcommands got lost in the dust.
http://bugs.python.org/issue9253#msg186387
There I suggest this work around, setting the required attribute after the subparsers is defined.
parser = ArgumentParser(prog='test')
subparsers = parser.add_subparsers()
subparsers.required = True
subparsers.dest = 'command'
subparser = subparsers.add_parser("foo", help="run foo")
parser.parse_args()
update
A related pull-request: https://github.com/python/cpython/pull/3027
In addition to hpaulj's answer: you can also use the required keyword argument with ArgumentParser.add_subparsers() since Python 3.7. You also need to pass dest as argument. Otherwise you will get an error: TypeError: sequence item 0: expected str instance, NoneType found.
Example file example.py:
import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(dest='command', required=True)
foo_parser = subparsers.add_parser("foo", help="command foo")
args = parser.parse_args()
Output of the call without an argument:
$ python example.py
usage: example.py [-h] {foo} ...
example.py: error: the following arguments are required: command
How about using required=True? More info here.
You can use the dest argument, which is documented in the last example in the documentation for add_subparsers():
# required_subparser.py
import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(dest='subparser_name')
one = subparsers.add_parser('one')
two = subparsers.add_parser('two')
args = parser.parse_args()
Running with Python 2.7:
$python required_subparser.py
usage: required_subparser.py [-h] {one,two} ...
required_subparser.py: error: too few arguments
$python required_subparser.py one
$# no error
I'm trying to write a program that supports arbitrary bitwise opertions: AND, OR, NOT and COUNT for bitmaps. The usage is that you run program.py --and f1.bit f2.bit and it prints you the result to the stdout.
The problem is that I'd like the parser to handle all the caveats. Specifically, I'd like the nargs to depend on the mode that's set - if it's set to COUNT or NOT, exactly one file is expected, if it's set to OR or AND, expect exactly two. Here's some (non-working) example code:
#!/usr/bin/env python
import argparse
def main(mode, fnames):
pass
if __name__ == '__main__':
parser = argparse.ArgumentParser()
parser.add_argument('-O', '--or',
nargs=2,
action='store_const', const='or'
)
args = parser.parse_args()
import pprint
pprint.pprint(args.__dict__)
#main(**args.__dict__)
And the error I'm getting:
Traceback (most recent call last):
File "bitmaptool.py", line 12, in <module>
action='store_const', const='or'
File "/usr/lib/python3.7/argparse.py", line 1362, in add_argument
action = action_class(**kwargs)
TypeError: __init__() got an unexpected keyword argument 'nargs'
Commenting out nargs helps, as does leaving nargs out but commenting out action - but I want both. Do I need to implement it manually or is there a trick or another library that would let me get there?
EDIT I wanted to clarify what I'm looking for by showing what code I needed to write manually for the thing to work:
if __name__ == '__main__':
parser = argparse.ArgumentParser(argument_default=argparse.SUPPRESS)
parser.add_argument('-O', '--or', nargs=2)
parser.add_argument('-A', '--and', nargs=2)
parser.add_argument('-M', '--minus', nargs=2)
parser.add_argument('-C', '--count', nargs=1)
parser.add_argument('-N', '--not', nargs=1)
parser.add_argument('-o', '--output', default='/dev/stdout')
args = parser.parse_args().__dict__
mode = None
files = []
for current_mode in ['or', 'and', 'not', 'count']:
if current_mode in args:
if mode is not None:
sys.exit('ERROR: more than one mode was specified')
mode = current_mode
files = args[mode]
if mode is None:
sys.stderr.write('ERROR: no mode was specified\n\n')
parser.print_help()
sys.exit(1)
import pprint
pprint.pprint(args)
Is there a more elegant way to get there?
store_const never gets arguments, it literally stores what you stated as const or None. Because it's a constant, not a variable. From the argparse's action documentation, ephasis mine:
'store_const' - This stores the value specified by the const keyword argument. The 'store_const' action is most commonly used with optional arguments that specify some sort of flag.
You should change the action to something that will actually store the filenames passed. As per argparse's nargs documentation and example, you actually don't need to specify action at all, default (action='store') will suffice.
Example from documentation:
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', nargs=2) #this line
>>> parser.add_argument('bar', nargs=1)
>>> parser.parse_args('c --foo a b'.split())
Namespace(bar=['c'], foo=['a', 'b'])
EDIT for the edited version of the question - mutually exclusive group will make sure only one argument (from that group, of course) is specified:
if __name__ == '__main__':
parser = argparse.ArgumentParser(argument_default=argparse.SUPPRESS)
parser.add_argument('-o', '--output', default='/dev/stdout')
group = parser.add_mutually_exclusive_group(required=True)
group.add_argument('-O', '--or', nargs=2)
group.add_argument('-A', '--and', nargs=2)
group.add_argument('-M', '--minus', nargs=2)
group.add_argument('-C', '--count', nargs=1)
group.add_argument('-N', '--not', nargs=1)
args = parser.parse_args().__dict__
import pprint
pprint.pprint(args)
I cant see m to figure out how to iterate over the accepted args of argparse. I get I can iterate over the parsed_args result, but what I want is to iterate over the arguments the parser is configured with ( ie with optparse you can iterate over the args ).
for example:
parser = argparse.ArgumentParser( prog = 'myapp' )
parser.add_argument( '--a', .. )
parser.add_argument( '--b', ...)
parser.add_argument( '--c', ... )
for arg in parser.args():
print arg
would result in
--a
--b
--c
You'll probably want to getattr from the args:
args = parser.parse_args()
for arg in vars(args):
print arg, getattr(args, arg)
Result:
a None
c None
b None
If you want to list the optionals you can do it this way:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--foo')
parser.add_argument('--bar')
parser.add_argument('--baz')
for option in parser._optionals._actions:
print(option.option_strings)
I don't see a practical reason to iterate over them however. You can always see the options via --help.
A bit late to the game here, but I found a way to do this without reading from private variables by using a custom help formatter that collects the arguments it is asked to format.
The following program will print ['-h', '--help', '--a', '--b', '--c']
import argparse
class ArgCollector(argparse.HelpFormatter):
# Will store the arguments in a class variable since argparse uses a class
# name, not an instance of a class
args = []
def add_argument(self, action):
# Just remember the options
self.args.extend(action.option_strings)
def main():
parser = argparse.ArgumentParser()
parser.add_argument('--a')
parser.add_argument('--b')
parser.add_argument('--c')
# Install our new help formatter, use it, then restore the original
# formatter
original_formatter_class = parser.formatter_class
parser.formatter_class = ArgCollector
parser.format_help()
parser.formatter_class = original_formatter_class
# Print the args that argparse would accept
print(ArgCollector.args)
if __name__ == '__main__':
main()
I have the following code (using Python 2.7):
# shared command line options, like --version or --verbose
parser_shared = argparse.ArgumentParser(add_help=False)
parser_shared.add_argument('--version', action='store_true')
# the main parser, inherits from `parser_shared`
parser = argparse.ArgumentParser(description='main', parents=[parser_shared])
# several subcommands, which can't inherit from the main parser, since
# it would expect subcommands ad infinitum
subparsers = parser.add_subparsers('db', parents=[parser_shared])
...
args = parser.parse_args()
Now I would like to be able to call this program e.g. with the --version appended to the normal program or some subcommand:
$ prog --version
0.1
$ prog db --version
0.1
Basically, I need to declare optional subparsers. I'm aware that this isn't really supported, but are there any workarounds or alternatives?
Edit: The error message I am getting:
$ prog db --version
# works fine
$ prog --version
usage: ....
prog: error: too few arguments
According to documentation, --version with action='version' (and not with action='store_true') prints automatically the version number:
parser.add_argument('--version', action='version', version='%(prog)s 2.0')
FWIW, I ran into this also, and ended up "solving" it by not using subparsers (I already had my own system for printing help, so didn't lose anything there).
Instead, I do this:
parser.add_argument("command", nargs="?",
help="name of command to execute")
args, subcommand_args = parser.parse_known_args()
...and then the subcommand creates its own parser (similar to a subparser) which operates only on subcommand_args.
This seems to implement the basic idea of an optional subparser. We parse the standard arguments that apply to all subcommands. Then, if anything is left, we invoke the parser on the rest. The primary arguments are a parent of the subcommand so the -h appears correctly. I plan to enter an interactive prompt if no subcommands are present.
import argparse
p1 = argparse.ArgumentParser( add_help = False )
p1.add_argument( ‘–flag1′ )
p2 = argparse.ArgumentParser( parents = [ p1 ] )
s = p2.add_subparsers()
p = s.add_parser( ‘group’ )
p.set_defaults( group=True )
( init_ns, remaining ) = p1.parse_known_args( )
if remaining:
p2.parse_args( args = remaining, namespace=init_ns )
else:
print( ‘Enter interactive loop’ )
print( init_ns )
As discussed in http://bugs.python.org/issue9253 (argparse: optional subparsers), as of Python 3.3, subparsers are now optional. This was an unintended result of a change in how parse_args checked for required arguments.
I found a fudge that restores the previous (required subparsers) behavior, explicitly setting the required attribute of the subparsers action.
parser = ArgumentParser(prog='test')
subparsers = parser.add_subparsers()
subparsers.required = True # the fudge
subparsers.dest = 'command'
subparser = subparsers.add_parser("foo", help="run foo")
parser.parse_args()
See that issue for more details. I expect that if and when this issue gets properly patched, subparsers will be required by default, with some sort of option to set its required attribute to False. But there is a big backlog of argparse patches.
Yeah, I just checked svn, which is used as an object example in the add_subparsers() documentation, and it only supports '--version' on the main command:
python zacharyyoung$ svn log --version
Subcommand 'log' doesn't accept option '--version'
Type 'svn help log' for usage.
Still:
# create common parser
parent_parser = argparse.ArgumentParser('parent', add_help=False)
parent_parser.add_argument('--version', action='version', version='%(prog)s 2.0')
# create the top-level parser
parser = argparse.ArgumentParser(parents=[parent_parser])
subparsers = parser.add_subparsers()
# create the parser for the "foo" command
parser_foo = subparsers.add_parser('foo', parents=[parent_parser])
Which yields:
python zacharyyoung$ ./arg-test.py --version
arg-test.py 2.0
python zacharyyoung$ ./arg-test.py foo --version
arg-test.py foo 2.0
While we wait for this feature to be delivered, we can use code like this:
# Make sure that main is the default sub-parser
if '-h' not in sys.argv and '--help' not in sys.argv:
if len(sys.argv) < 2:
sys.argv.append('main')
if sys.argv[1] not in ('main', 'test'):
sys.argv = [sys.argv[0], 'main'] + sys.argv[1:]
Although #eumiro's answer address the --version option, it can only do so because that is a special case for optparse. To allow general invocations of:
prog
prog --verbose
prog --verbose main
prog --verbose db
and have prog --version work the same as prog --verbose main (and prog main --verbose) you can add a method to Argumentparser and call that with the name of the default subparser, just before invoking parse_args():
import argparse
import sys
def set_default_subparser(self, name, args=None):
"""default subparser selection. Call after setup, just before parse_args()
name: is the name of the subparser to call by default
args: if set is the argument list handed to parse_args()
, tested with 2.7, 3.2, 3.3, 3.4
it works with 2.6 assuming argparse is installed
"""
subparser_found = False
for arg in sys.argv[1:]:
if arg in ['-h', '--help']: # global help if no subparser
break
else:
for x in self._subparsers._actions:
if not isinstance(x, argparse._SubParsersAction):
continue
for sp_name in x._name_parser_map.keys():
if sp_name in sys.argv[1:]:
subparser_found = True
if not subparser_found:
# insert default in first position, this implies no
# global options without a sub_parsers specified
if args is None:
sys.argv.insert(1, name)
else:
args.insert(0, name)
argparse.ArgumentParser.set_default_subparser = set_default_subparser
def do_main(args):
print 'main verbose', args.verbose
def do_db(args):
print 'db verbose:', args.verbose
parser = argparse.ArgumentParser()
parser.add_argument('--verbose', action='store_true')
parser.add_argument('--version', action='version', version='%(prog)s 2.0')
subparsers = parser.add_subparsers()
sp = subparsers.add_parser('main')
sp.set_defaults(func=do_main)
sp.add_argument('--verbose', action='store_true')
sp = subparsers.add_parser('db')
sp.set_defaults(func=do_db)
parser.set_default_subparser('main')
args = parser.parse_args()
if hasattr(args, 'func'):
args.func(args)
The set_default_subparser() method is part of the ruamel.std.argparse package.