I'm trying to build a command line interface with Python's argparse module. I want two positional arguments where one depends on the other (mutually inclusive). Here is what I want:
prog [arg1 [arg2]]
Here's what I have so far:
prog [arg1] [arg2]
Which is produced by:
parser = argparse.ArgumentParser()
parser.add_argument('arg1', nargs='?')
parser.add_argument('arg2', nargs='?')
How do I get from there to having a mutually inclusive arg2?
Module argparse doesn't have options for creating mutually inclusive arguments.
However it's simple to write it by yourself.
Start with adding both arguments as optional:
parser.add_argument('arg1', nargs='?')
parser.add_argument('arg2', nargs='?')
After parsing arguments check if arg1 is set and arg2 is not:
args = parser.parse_args()
if args.arg1 and not args.arg2:
(this may be more tricky if you change default value from None for not used arguments to something different)
Then use parser.error() function to display normal argparse error message:
parser.error('the following arguments are required: arg2')
Finally change usage: message to show that arg2 depends on arg1:
parser = argparse.ArgumentParser(usage='%(prog)s [arg1 [arg2]]')
A complete script:
import argparse
parser = argparse.ArgumentParser(usage='%(prog)s [arg1 [arg2]]')
parser.add_argument('arg1', nargs='?')
parser.add_argument('arg2', nargs='?')
args = parser.parse_args()
if args.arg1 and not args.arg2:
parser.error('the following arguments are required: arg2')
You can do something similar to this using sub_parsers.
Here are the docs and examples:
http://docs.python.org/2/library/argparse.html#sub-commands
Related
In this example script
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--modes', help="test", nargs='+', type=str)
args = parser.parse_args()
write_mode = args.modes
print(write_mode)
There is only one argument modes.
However, python test.py --modes sdfsf and python test.py --mode sdfsf give me the same output (['sdfsf']) which means the parser treats mode as modes.
Is this a bug of argparse?
This is an example of prefix matching, which is allowed by argparse by default.
Turn it off by using argparse.ArgumentParser(..., allow_abbrev=False).
I need to implement a command line interface in which the program accepts subcommands.
For example, if the program is called “foo”, the CLI would look like
foo cmd1 <cmd1-options>
foo cmd2
foo cmd3 <cmd3-options>
cmd1 and cmd3 must be used with at least one of their options and the three cmd* arguments are always exclusive.
I am trying to use subparsers in argparse, but with no success for the moment. The problem is with cmd2, that has no arguments:
if I try to add the subparser entry with no arguments, the namespace returned by parse_args will not contain any information telling me that this option was selected (see the example below).
if I try to add cmd2 as an argument to the parser (not the subparser), then argparse will expect that the cmd2 argument will be followed by any of the subparsers arguments.
Is there a simple way to achieve this with argparse? The use case should be quite common…
Here follows what I have attempted so far that is closer to what I need:
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='Functions')
parser_1 = subparsers.add_parser('cmd1', help='...')
parser_1.add_argument('cmd1_option1', type=str, help='...')
parser_2 = subparsers.add_parser(cmd2, help='...')
parser_3 = subparsers.add_parser('cmd3', help='...')
parser_3.add_argument('cmd3_options', type=int, help='...')
args = parser.parse_args()
First of all subparsers are never inserted in the namespace. In the example you posted if you try to run the script as:
$python3 test_args.py cmd1 1
Namespace(cmd1_option1='1')
where test_args.py contain the code you provided (with the import argparse at the beginning and print(args) at the end).
Note that there is no mention to cmd1 only to its argument. This is by design.
As pointed out in the comments you can add that information passing the dest argument to the add_subparsers call.
The usual way to handle these circumstances is to use the set_defaults method of the subparsers:
import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='Functions')
parser_1 = subparsers.add_parser('cmd1', help='...')
parser_1.add_argument('cmd1_option1', type=str, help='...')
parser_1.set_defaults(parser1=True)
parser_2 = subparsers.add_parser('cmd2', help='...')
parser_2.set_defaults(parser2=True)
parser_3 = subparsers.add_parser('cmd3', help='...')
parser_3.add_argument('cmd3_options', type=int, help='...')
parser_3.set_defaults(parser_3=True)
args = parser.parse_args()
print(args)
Which results in:
$python3 test_args.py cmd1 1
Namespace(cmd1_option1='1', parser1=True)
$python3 test_args.py cmd2
Namespace(parser2=True)
In general different subparser will, most of the time, handle the arguments in completely different ways. The usual pattern is to have different functions to run the different commands and use set_defaults to set a func attribute. When you parse the arguments you simply call that callable:
subparsers = parser.add_subparsers()
parser_1 = subparsers.add_parser(...)
parser_1.set_defaults(func=do_command_one)
parser_k = subparsers.add_parser(...)
parser_k.set_defaults(func=do_command_k)
args = parser.parse_args()
if args.func:
args.func(args)
The subparser identity can be added to the main Namespace if the add_subparsers command is given a dest.
From the documentation:
However, if it is necessary to check the name of the subparser that was invoked, the dest keyword argument to the add_subparsers() call will work:
>>> parser = argparse.ArgumentParser()
>>> subparsers = parser.add_subparsers(dest='subparser_name')
>>> subparser1 = subparsers.add_parser('1')
>>> subparser1.add_argument('-x')
>>> subparser2 = subparsers.add_parser('2')
>>> subparser2.add_argument('y')
>>> parser.parse_args(['2', 'frobble'])
Namespace(subparser_name='2', y='frobble')
By default the dest is argparse.SUPPRESS, which keeps subparsers from adding the name to the namespace.
In Python's argparse, how do you implement top-level arguments while still using commands implemented as subparsers?
I'm trying to implement a --version argument to show the program's version number, but argparse is giving me error: too few arguments because I'm not specifying a sub-command for one of the subparsers.
My code:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument(
'-v', '--version',
help='Show version.',
action='store_true',
default=False
)
subparsers = parser.add_subparsers(
dest="command",
)
list_parser = subparsers.add_parser('list')
parser.parse_args(['--version'])
the output:
usage: myscript.py [-h] [-v] {list} ...
myscript.py: error: too few arguments
If you only need version to work, you can do this:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument(
'-v', '--version',
action='version',
version='%(prog)s 1.0',
)
Subparsers won't bother any more; the special version action is processed and exits the script before the parser looks for subcommands.
The subparsers is a kind of positional argument. So normally that's required (just as though you'd specified add_argument('foo')).
skyline's suggestion works because action='version' is an action class that exits after displaying its information, just like the default -h.
There is bug/feature in the latest argparse that makes subparsers optional. Depending on how that is resolved, it may be possible in the future to give the add_subparsers command a required=False parameter. But the intended design is that subparsers will be required, unless a flagged argument (like '-h') short circuits the parsing.
I need to implement a command line interface in which the program accepts subcommands.
For example, if the program is called “foo”, the CLI would look like
foo cmd1 <cmd1-options>
foo cmd2
foo cmd3 <cmd3-options>
cmd1 and cmd3 must be used with at least one of their options and the three cmd* arguments are always exclusive.
I am trying to use subparsers in argparse, but with no success for the moment. The problem is with cmd2, that has no arguments:
if I try to add the subparser entry with no arguments, the namespace returned by parse_args will not contain any information telling me that this option was selected (see the example below).
if I try to add cmd2 as an argument to the parser (not the subparser), then argparse will expect that the cmd2 argument will be followed by any of the subparsers arguments.
Is there a simple way to achieve this with argparse? The use case should be quite common…
Here follows what I have attempted so far that is closer to what I need:
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='Functions')
parser_1 = subparsers.add_parser('cmd1', help='...')
parser_1.add_argument('cmd1_option1', type=str, help='...')
parser_2 = subparsers.add_parser(cmd2, help='...')
parser_3 = subparsers.add_parser('cmd3', help='...')
parser_3.add_argument('cmd3_options', type=int, help='...')
args = parser.parse_args()
First of all subparsers are never inserted in the namespace. In the example you posted if you try to run the script as:
$python3 test_args.py cmd1 1
Namespace(cmd1_option1='1')
where test_args.py contain the code you provided (with the import argparse at the beginning and print(args) at the end).
Note that there is no mention to cmd1 only to its argument. This is by design.
As pointed out in the comments you can add that information passing the dest argument to the add_subparsers call.
The usual way to handle these circumstances is to use the set_defaults method of the subparsers:
import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='Functions')
parser_1 = subparsers.add_parser('cmd1', help='...')
parser_1.add_argument('cmd1_option1', type=str, help='...')
parser_1.set_defaults(parser1=True)
parser_2 = subparsers.add_parser('cmd2', help='...')
parser_2.set_defaults(parser2=True)
parser_3 = subparsers.add_parser('cmd3', help='...')
parser_3.add_argument('cmd3_options', type=int, help='...')
parser_3.set_defaults(parser_3=True)
args = parser.parse_args()
print(args)
Which results in:
$python3 test_args.py cmd1 1
Namespace(cmd1_option1='1', parser1=True)
$python3 test_args.py cmd2
Namespace(parser2=True)
In general different subparser will, most of the time, handle the arguments in completely different ways. The usual pattern is to have different functions to run the different commands and use set_defaults to set a func attribute. When you parse the arguments you simply call that callable:
subparsers = parser.add_subparsers()
parser_1 = subparsers.add_parser(...)
parser_1.set_defaults(func=do_command_one)
parser_k = subparsers.add_parser(...)
parser_k.set_defaults(func=do_command_k)
args = parser.parse_args()
if args.func:
args.func(args)
The subparser identity can be added to the main Namespace if the add_subparsers command is given a dest.
From the documentation:
However, if it is necessary to check the name of the subparser that was invoked, the dest keyword argument to the add_subparsers() call will work:
>>> parser = argparse.ArgumentParser()
>>> subparsers = parser.add_subparsers(dest='subparser_name')
>>> subparser1 = subparsers.add_parser('1')
>>> subparser1.add_argument('-x')
>>> subparser2 = subparsers.add_parser('2')
>>> subparser2.add_argument('y')
>>> parser.parse_args(['2', 'frobble'])
Namespace(subparser_name='2', y='frobble')
By default the dest is argparse.SUPPRESS, which keeps subparsers from adding the name to the namespace.
import argparse
parser = argparse.ArgumentParser()
parser.add_argument(
'--optional',
default=None,
const='some-const',
nargs='?',
help='optional')
subparsers = parser.add_subparsers()
subparser = subparsers.add_parser('subparser')
subparser.add_argument(
'positional',
help='positional')
args = parser.parse_args()
print args
./test.py --optional opt subparser positional
Namespace(optional='opt', positional='positional') <-- works as expected
./test.py --optional subparser positional
usage: test.py [-h] [--optional [OPTIONAL]] {subparser} ...
test.py: error: invalid choice: 'positional' (choose from 'subparser') <-- throws an error
Namespace(optional='some-const', positional='positional') <-- would expect to see this
Above is my simplest test code to demonstrate this problem. I would like to have an optional arg using nargs='?' and const before my positional arg in the subparser. I have read that I can pass the original parser as a parent to the child subparser, but this doesn't solve the problem. I have tried adding add_help=False and conflict_handler='resolve' to the initial parser declaration when I tried that. Can anyone point me in the right direction on this?
Thanks,
Scott
When parsing ./test.py --optional foo bar, argparse sees an optional string (starts with --) followed by two argument strings (no --)
So it starts by processing --optional. It's nargs is a 'greedy ?', so it consumes the foo argument, producing:
Namespace('optional'='foo')
That leaves bar to be consumed as a subcommand argument.
It does not check if foo is a valid subcommand argument.
The same reasoning applies to ./test.py --optional subparser positional.
This throws an error:
.test.py --optional
Because subparser is not optional:
usage: subparser.py [-h] [--optional [OPTIONAL]] {subparser} ...
test.py: error: too few arguments
subparser is getting eaten up and used as OPTIONAL in your second example. I don't understand why, other than argparse isn't figuring out in advance that subparser is a subparser.
This is the closest thing I could make to what you are describing:
import argparse
parent_parser = argparse.ArgumentParser(add_help=False)
parent_parser.add_argument(
'--optional',
nargs='?',
default=None,
const='some-const',
help='optional')
sub_parser = argparse.ArgumentParser(parents=[parent_parser])
sub_parser.add_argument('--subparser', required=True)
args = sub_parser.parse_args()
print args
I think you've uncovered a bug.