问题
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()
回答1:
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_default(func=do_command_one)
parser_k = subparsers.add_parser(...)
parser_k.set_default(func=do_command_k)
args = parser.parse_args()
if args.func:
args.func(args)
回答2:
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
.
来源:https://stackoverflow.com/questions/26216875/how-to-handle-cli-subcommands-with-argparse