问题
I'm using Python 2.7 and I'm trying to accomplish a shell like behavior using argparse. My issue, in general, that I cannot seem to find a way, in Python 2.7, to use argparse's subparsers as optional. It's kind of hard to explain my issue so I'll describe what I require from my program.
The program has 2 modes of work:
- Starting the program with a given command (each command has it's own additional arguments) and additional arguments will run a specific task.
- Starting the program without a command will start a shell-like program that can take a line of arguments and process them as if the program was called with the given line as it's arguments.
So, if for example my program supports 'cmd1' and 'cmd2' commands, I could use it like so:
python program.py cmd1 additional_args1
python program.py cmd2 additional_args2
or with shell mode:
python program.py
cmd1 additional_args1
cmd2 additional_args2
quit
In addition, I also want my program to be able to take optional global arguments that will effect all commands.
For that I'm using argparse like so (This is a pure example):
parser = argparse.ArgumentParser(description="{} - Version {}".format(PROGRAM_NAME, PROGRAM_VERSION))
parser.add_argument("-i", "--info", help="Display more information")
subparsers = parser.add_subparsers()
parserCmd1 = subparsers.add_parser("cmd1", help="First Command")
parserCmd1.set_defaults(func=cmd1)
parserCmd2 = subparsers.add_parser("cmd2", help="Second Command")
parserCmd2.add_argument("-o", "--output", help="Redirect Output")
parserCmd2.set_defaults(func=cmd2)
So I can call cmd1 (with no additional args) or cmd2 (with or without -o flag). And for both I can add flag -i to display even more information of the called command.
My issue is that I cannot activate shell mode, because I have to provide cmd1 or cmd2 as an argument (because of using subparsers which are mandatory)
Restrictions:
- I cannot use Python 3 (I know it can be easily done there)
- Because of global optional arguments I cannot check to see if I get no arguments to skip arg parsing.
- I don't want to add a new command to call shell, it must be when providing no command at all
So how can I achieve This kind of behavior with argparse and python 2.7?
回答1:
Another idea is to use a 2 stage parsing. One handles 'globals', returning strings it can't handle. Then conditionally handle the extras with subparsers.
import argparse
def cmd1(args):
print('cmd1', args)
def cmd2(args):
print('cmd2', args)
parser1 = argparse.ArgumentParser()
parser1.add_argument("-i", "--info", help="Display more information")
parser2 = argparse.ArgumentParser()
subparsers = parser2.add_subparsers(dest='cmd')
parserCmd1 = subparsers.add_parser("cmd1", help="First Command")
parserCmd1.set_defaults(func=cmd1)
parserCmd2 = subparsers.add_parser("cmd2", help="Second Command")
parserCmd2.add_argument("-o", "--output", help="Redirect Output")
parserCmd2.set_defaults(func=cmd2)
args, extras = parser1.parse_known_args()
if len(extras)>0 and extras[0] in ['cmd1','cmd2']:
args = parser2.parse_args(extras, namespace=args)
args.func(args)
else:
print('doing system with', args, extras)
sample runs:
0901:~/mypy$ python stack46667843.py -i info
('doing system with', Namespace(info='info'), [])
0901:~/mypy$ python stack46667843.py -i info extras for sys
('doing system with', Namespace(info='info'), ['extras', 'for', 'sys'])
0901:~/mypy$ python stack46667843.py -i info cmd1
('cmd1', Namespace(cmd='cmd1', func=<function cmd1 at 0xb74b025c>, info='info'))
0901:~/mypy$ python stack46667843.py -i info cmd2 -o out
('cmd2', Namespace(cmd='cmd2', func=<function cmd2 at 0xb719ebc4>, info='info', output='out'))
0901:~/mypy$
回答2:
A bug/issue (with links) on the topic of 'optional' subparsers.
https://bugs.python.org/issue29298
Notice that this has a recent pull request.
With your script and the addition of
args = parser.parse_args()
print(args)
results are
1008:~/mypy$ python3 stack46667843.py
Namespace(info=None)
1009:~/mypy$ python2 stack46667843.py
usage: stack46667843.py [-h] [-i INFO] {cmd1,cmd2} ...
stack46667843.py: error: too few arguments
1009:~/mypy$ python2 stack46667843.py cmd1
Namespace(func=<function cmd1 at 0xb748825c>, info=None)
1011:~/mypy$ python3 stack46667843.py cmd1
Namespace(func=<function cmd1 at 0xb7134dac>, info=None)
I thought the 'optional' subparsers affected both Py2 and 3 versions, but apparently it doesn't. I'll have to look at the code to verify why.
In both languages, subparsers.required
is False
. If I set it to true
subparsers.required=True
(and add a dest
to the subparsers definition), the PY3 error message is
1031:~/mypy$ python3 stack46667843.py
usage: stack46667843.py [-h] [-i INFO] {cmd1,cmd2} ...
stack46667843.py: error: the following arguments are required: cmd
So there's a difference in how the 2 versions test for required
arguments. Py3 pays attention to the required
attribute; Py2 (apparently) uses the earlier method of checking whether the positionals
list is empty or not.
Checking for required arguments occurs near the end of parser._parse_known_args
.
Python2.7 includes
# if we didn't use all the Positional objects, there were too few
# arg strings supplied.
if positionals:
self.error(_('too few arguments'))
before the iteration that checks action.required
. That's what's catching the missing cmd
and saying too few arguments
.
So a kludge is to edit your argparse.py
and remove that block so it matches the corresponding section of the Py3 version.
来源:https://stackoverflow.com/questions/46667843/how-to-set-a-default-subparser-using-argparse-module-with-python-2-7