Can't get argparse to read quoted string with dashes in it?
Question:
Is there a way to make argparse recognize anything between two quotes as a single argument? It seems to keep seeing the dashes and assuming that it’s the start of a new option
I have something like:
mainparser = argparse.ArgumentParser()
subparsers = mainparser.add_subparsers(dest='subcommand')
parser = subparsers.add_parser('queue')
parser.add_argument('-env', '--extraEnvVars', type=str,
help='String of extra arguments to be passed to model.')
...other arguments added to parser...
But when I run:
python Application.py queue -env "-s WHATEVER -e COOL STUFF"
It gives me:
Application.py queue: error: argument -env/--extraEnvVars: expected one argument
If I leave off the first dash, it works totally fine, but it’s kind of crucial that I be able to pass in a string with dashes in it. I’ve tried escaping it with , which causes it to succeed but adds the to the argument string Does anyone know how to get around this? This happens whether or not -s is an argument in parser.
EDIT: I’m using Python 2.7.
EDIT2:
python Application.py -env " -env"
works perfectly fine, but
python Application.py -env "-env"
does not.
EDIT3: Looks like this is actually a bug that’s being debated already: http://www.gossamer-threads.com/lists/python/bugs/89529, http://python.6.x6.nabble.com/issue9334-argparse-does-not-accept-options-taking-arguments-beginning-with-dash-regression-from-optp-td578790.html. It’s only in 2.7 and not in optparse.
EDIT4: The current open bug report is: http://bugs.python.org/issue9334
Answers:
Updated answer:
You can put an equals sign when you call it:
python Application.py -env="-env"
Original answer:
I too have had troubles doing what you are trying to do, but there is a workaround build into argparse, which is the parse_known_args method. This will let all arguments that you haven’t defined pass through the parser with the assumption that you would use them for a subprocess. The drawbacks are that you won’t get error reporting with bad arguments, and you will have to make sure that there is no collision between your options and your subprocess’s options.
Another option could be to force the user’s to use a plus instead of a minus:
python Application.py -e "+s WHATEVER +e COOL STUFF"
and then you change the ‘+’ to ‘-‘ in post processing before passing to your subprocess.
You can start the argument with a space python tst.py -e ' -e blah'
as a very simple workaround. Simply lstrip()
the option to put it back to normal, if you like.
Or, if the first “sub-argument” is not also a valid argument to the original function then you shouldn’t need to do anything at all. That is, the only reason that python tst.py -e '-s hi -e blah'
doesn’t work is because -s
is a valid option to tst.py
.
Also, the optparse module, now deprecated, works without any issue.
This issue is discussed in depth in http://bugs.python.org/issue9334. Most of the activity was in 2011. I added a patch last year, but there’s quite a backlog of argparse
patches.
At issue is the potential ambiguity in a string like '--env'
, or "-s WHATEVER -e COOL STUFF"
when it follows an option that takes an argument.
optparse
does a simple left to right parse. The first --env
is an option flag that takes one argument, so it consumes the next, regardless of what it looks like. argparse
, on the other hand, loops through the strings twice. First it categorizes them as ‘O’ or ‘A’ (option flag or argument). On the second loop it consumes them, using a re
like pattern matching to handle variable nargs
values. In this case it looks like we have OO
, two flags and no arguments.
The solution when using argparse
is to make sure an argument string will not be confused for an option flag. Possibilities that have been shown here (and in the bug issue) include:
--env="--env" # clearly defines the argument.
--env " --env" # other non - character
--env "--env " # space after
--env "--env one two" # but not '--env "-env one two"'
By itself '--env'
looks like a flag (even when quoted, see sys.argv
), but when followed by other strings it does not. But "-env one two"
has problems because it can be parsed as ['-e','nv one two']
, a `’-e’ flag followed by a string (or even more options).
--
and nargs=argparse.PARSER
can also be used to force argparse
to view all following strings as arguments. But they only work at the end of argument lists.
There is a proposed patch in issue9334 to add a args_default_to_positional=True
mode. In this mode, the parser only classifies strings as option flags if it can clearly match them with defined arguments. Thus ‘–one’ in ‘–env –one’ would be classed as as an argument. But the second ‘–env’ in ‘–env –env’ would still be classed as an option flag.
Expanding on the related case in
Using argparse with argument values that begin with a dash ("-")
parser = argparse.ArgumentParser(prog="PROG")
parser.add_argument("-f", "--force", default=False, action="store_true")
parser.add_argument("-e", "--extra")
args = parser.parse_args()
print(args)
produces
1513:~/mypy$ python3 stack16174992.py --extra "--foo one"
Namespace(extra='--foo one', force=False)
1513:~/mypy$ python3 stack16174992.py --extra "-foo one"
usage: PROG [-h] [-f] [-e EXTRA]
PROG: error: argument -e/--extra: expected one argument
1513:~/mypy$ python3 stack16174992.py --extra "-bar one"
Namespace(extra='-bar one', force=False)
1514:~/mypy$ python3 stack16174992.py -fe one
Namespace(extra='one', force=True)
The “-foo one” case fails because the -foo
is interpreted as the -f
flag plus unspecified extras. This is the same action that allows -fe
to be interpreted as ['-f','-e']
.
If I change the nargs
to REMAINDER
(not PARSER
), everything after -e
is interpreted as arguments for that flag:
parser.add_argument("-e", "--extra", nargs=argparse.REMAINDER)
All cases work. Note the value is a list. And quotes are not needed:
1518:~/mypy$ python3 stack16174992.py --extra "--foo one"
Namespace(extra=['--foo one'], force=False)
1519:~/mypy$ python3 stack16174992.py --extra "-foo one"
Namespace(extra=['-foo one'], force=False)
1519:~/mypy$ python3 stack16174992.py --extra "-bar one"
Namespace(extra=['-bar one'], force=False)
1519:~/mypy$ python3 stack16174992.py -fe one
Namespace(extra=['one'], force=True)
1520:~/mypy$ python3 stack16174992.py --extra --foo one
Namespace(extra=['--foo', 'one'], force=False)
1521:~/mypy$ python3 stack16174992.py --extra -foo one
Namespace(extra=['-foo', 'one'], force=False)
argparse.REMAINDER
is like ‘*’, except it takes everything that follows, whether it looks like a flag or not. argparse.PARSER
is more like ‘+’, in that it expects a positional
like argument first. It’s the nargs
that subparsers
uses.
This uses of REMAINDER
is documented, https://docs.python.org/3/library/argparse.html#nargs
paser.add_argument("--argument_name", default=None, nargs=argparse.REMAINDER)
python_file.py –argument_name “–abc=10 -a=1 -b=2 cdef”
Note: the argument values have to be passed only within double quotes and this doesn’t work with single quotes
I have ported a script from optparse to argparse, where certain arguments took values that could start with a negative number. I ran into this problem because the script is used in many places without using the ‘=’ sign to join negative values to the flag. After reading the discussion here and in http://bugs.python.org/issue9334, I know the arguments only take one value and there was no risk in accepting a succeeding argument (ie, a missing value) as the value. FWIW, my solution was to preprocess the arguments and join the problematic ones with ‘=’ before passing to parse_args():
def preprocess_negative_args(argv, flags=None):
if flags is None:
flags = ['--time', '--mtime']
result = []
i = 0
while i < len(argv):
arg = argv[i]
if arg in flags and i+1 < len(argv) and argv[i+1].startswith('-'):
arg = arg + "=" + argv[i+1]
i += 1
result.append(arg)
i += 1
return result
This approach at least does not require any user changes, and it only modifies the arguments which explicitly need to allow negative values.
>>> import argparse
>>> parser = argparse.ArgumentParser("prog")
>>> parser.add_argument("--time")
>>> parser.parse_args(preprocess_negative_args("--time -1d,2".split()))
Namespace(time='-1d,2')
It would be more convenient to tell argparse which arguments should explicitly allow values with a leading dash, but this approach seems like a reasonable compromise.
To bypass having to deal with argparse even looking at a ‘-‘ for something that isn’t a flag you want, you can edit sys.argv before argparse reads it. Just save the argument that you don’t want seen, put a filler argument in it’s place, and then replace the filler with the original after argparse process sys.argv. I just had to do this for my own code. It’s not pretty, but it works and it’s easy. You could also use a for loop to iterate through sys.argv if your flags aren’t always in the same order.
parser.add_argument('-n', '--input', nargs='*')
spot_saver = ''
if sys.argv[1] == '-n': #'-n' can be any flag you use
if sys.argv[2][0] == '-': #This checks the first character of the element
spot_saver = sys.argv[2]
sys.argv[2] = "fillerText"
args = parser.parse_args()
if args.input[0] == 'fillerText':
args.input[0] = spot_saver
Similar problem. And I solve this by replace space by " ". For example:
replace
python Application.py "cmd -option"
by
python Application.py "cmd -option"
.
Not sure for your problem.
Is there a way to make argparse recognize anything between two quotes as a single argument? It seems to keep seeing the dashes and assuming that it’s the start of a new option
I have something like:
mainparser = argparse.ArgumentParser()
subparsers = mainparser.add_subparsers(dest='subcommand')
parser = subparsers.add_parser('queue')
parser.add_argument('-env', '--extraEnvVars', type=str,
help='String of extra arguments to be passed to model.')
...other arguments added to parser...
But when I run:
python Application.py queue -env "-s WHATEVER -e COOL STUFF"
It gives me:
Application.py queue: error: argument -env/--extraEnvVars: expected one argument
If I leave off the first dash, it works totally fine, but it’s kind of crucial that I be able to pass in a string with dashes in it. I’ve tried escaping it with , which causes it to succeed but adds the to the argument string Does anyone know how to get around this? This happens whether or not -s is an argument in parser.
EDIT: I’m using Python 2.7.
EDIT2:
python Application.py -env " -env"
works perfectly fine, but
python Application.py -env "-env"
does not.
EDIT3: Looks like this is actually a bug that’s being debated already: http://www.gossamer-threads.com/lists/python/bugs/89529, http://python.6.x6.nabble.com/issue9334-argparse-does-not-accept-options-taking-arguments-beginning-with-dash-regression-from-optp-td578790.html. It’s only in 2.7 and not in optparse.
EDIT4: The current open bug report is: http://bugs.python.org/issue9334
Updated answer:
You can put an equals sign when you call it:
python Application.py -env="-env"
Original answer:
I too have had troubles doing what you are trying to do, but there is a workaround build into argparse, which is the parse_known_args method. This will let all arguments that you haven’t defined pass through the parser with the assumption that you would use them for a subprocess. The drawbacks are that you won’t get error reporting with bad arguments, and you will have to make sure that there is no collision between your options and your subprocess’s options.
Another option could be to force the user’s to use a plus instead of a minus:
python Application.py -e "+s WHATEVER +e COOL STUFF"
and then you change the ‘+’ to ‘-‘ in post processing before passing to your subprocess.
You can start the argument with a space python tst.py -e ' -e blah'
as a very simple workaround. Simply lstrip()
the option to put it back to normal, if you like.
Or, if the first “sub-argument” is not also a valid argument to the original function then you shouldn’t need to do anything at all. That is, the only reason that python tst.py -e '-s hi -e blah'
doesn’t work is because -s
is a valid option to tst.py
.
Also, the optparse module, now deprecated, works without any issue.
This issue is discussed in depth in http://bugs.python.org/issue9334. Most of the activity was in 2011. I added a patch last year, but there’s quite a backlog of argparse
patches.
At issue is the potential ambiguity in a string like '--env'
, or "-s WHATEVER -e COOL STUFF"
when it follows an option that takes an argument.
optparse
does a simple left to right parse. The first --env
is an option flag that takes one argument, so it consumes the next, regardless of what it looks like. argparse
, on the other hand, loops through the strings twice. First it categorizes them as ‘O’ or ‘A’ (option flag or argument). On the second loop it consumes them, using a re
like pattern matching to handle variable nargs
values. In this case it looks like we have OO
, two flags and no arguments.
The solution when using argparse
is to make sure an argument string will not be confused for an option flag. Possibilities that have been shown here (and in the bug issue) include:
--env="--env" # clearly defines the argument.
--env " --env" # other non - character
--env "--env " # space after
--env "--env one two" # but not '--env "-env one two"'
By itself '--env'
looks like a flag (even when quoted, see sys.argv
), but when followed by other strings it does not. But "-env one two"
has problems because it can be parsed as ['-e','nv one two']
, a `’-e’ flag followed by a string (or even more options).
--
and nargs=argparse.PARSER
can also be used to force argparse
to view all following strings as arguments. But they only work at the end of argument lists.
There is a proposed patch in issue9334 to add a args_default_to_positional=True
mode. In this mode, the parser only classifies strings as option flags if it can clearly match them with defined arguments. Thus ‘–one’ in ‘–env –one’ would be classed as as an argument. But the second ‘–env’ in ‘–env –env’ would still be classed as an option flag.
Expanding on the related case in
Using argparse with argument values that begin with a dash ("-")
parser = argparse.ArgumentParser(prog="PROG")
parser.add_argument("-f", "--force", default=False, action="store_true")
parser.add_argument("-e", "--extra")
args = parser.parse_args()
print(args)
produces
1513:~/mypy$ python3 stack16174992.py --extra "--foo one"
Namespace(extra='--foo one', force=False)
1513:~/mypy$ python3 stack16174992.py --extra "-foo one"
usage: PROG [-h] [-f] [-e EXTRA]
PROG: error: argument -e/--extra: expected one argument
1513:~/mypy$ python3 stack16174992.py --extra "-bar one"
Namespace(extra='-bar one', force=False)
1514:~/mypy$ python3 stack16174992.py -fe one
Namespace(extra='one', force=True)
The “-foo one” case fails because the -foo
is interpreted as the -f
flag plus unspecified extras. This is the same action that allows -fe
to be interpreted as ['-f','-e']
.
If I change the nargs
to REMAINDER
(not PARSER
), everything after -e
is interpreted as arguments for that flag:
parser.add_argument("-e", "--extra", nargs=argparse.REMAINDER)
All cases work. Note the value is a list. And quotes are not needed:
1518:~/mypy$ python3 stack16174992.py --extra "--foo one"
Namespace(extra=['--foo one'], force=False)
1519:~/mypy$ python3 stack16174992.py --extra "-foo one"
Namespace(extra=['-foo one'], force=False)
1519:~/mypy$ python3 stack16174992.py --extra "-bar one"
Namespace(extra=['-bar one'], force=False)
1519:~/mypy$ python3 stack16174992.py -fe one
Namespace(extra=['one'], force=True)
1520:~/mypy$ python3 stack16174992.py --extra --foo one
Namespace(extra=['--foo', 'one'], force=False)
1521:~/mypy$ python3 stack16174992.py --extra -foo one
Namespace(extra=['-foo', 'one'], force=False)
argparse.REMAINDER
is like ‘*’, except it takes everything that follows, whether it looks like a flag or not. argparse.PARSER
is more like ‘+’, in that it expects a positional
like argument first. It’s the nargs
that subparsers
uses.
This uses of REMAINDER
is documented, https://docs.python.org/3/library/argparse.html#nargs
paser.add_argument("--argument_name", default=None, nargs=argparse.REMAINDER)
python_file.py –argument_name “–abc=10 -a=1 -b=2 cdef”
Note: the argument values have to be passed only within double quotes and this doesn’t work with single quotes
I have ported a script from optparse to argparse, where certain arguments took values that could start with a negative number. I ran into this problem because the script is used in many places without using the ‘=’ sign to join negative values to the flag. After reading the discussion here and in http://bugs.python.org/issue9334, I know the arguments only take one value and there was no risk in accepting a succeeding argument (ie, a missing value) as the value. FWIW, my solution was to preprocess the arguments and join the problematic ones with ‘=’ before passing to parse_args():
def preprocess_negative_args(argv, flags=None):
if flags is None:
flags = ['--time', '--mtime']
result = []
i = 0
while i < len(argv):
arg = argv[i]
if arg in flags and i+1 < len(argv) and argv[i+1].startswith('-'):
arg = arg + "=" + argv[i+1]
i += 1
result.append(arg)
i += 1
return result
This approach at least does not require any user changes, and it only modifies the arguments which explicitly need to allow negative values.
>>> import argparse
>>> parser = argparse.ArgumentParser("prog")
>>> parser.add_argument("--time")
>>> parser.parse_args(preprocess_negative_args("--time -1d,2".split()))
Namespace(time='-1d,2')
It would be more convenient to tell argparse which arguments should explicitly allow values with a leading dash, but this approach seems like a reasonable compromise.
To bypass having to deal with argparse even looking at a ‘-‘ for something that isn’t a flag you want, you can edit sys.argv before argparse reads it. Just save the argument that you don’t want seen, put a filler argument in it’s place, and then replace the filler with the original after argparse process sys.argv. I just had to do this for my own code. It’s not pretty, but it works and it’s easy. You could also use a for loop to iterate through sys.argv if your flags aren’t always in the same order.
parser.add_argument('-n', '--input', nargs='*')
spot_saver = ''
if sys.argv[1] == '-n': #'-n' can be any flag you use
if sys.argv[2][0] == '-': #This checks the first character of the element
spot_saver = sys.argv[2]
sys.argv[2] = "fillerText"
args = parser.parse_args()
if args.input[0] == 'fillerText':
args.input[0] = spot_saver
Similar problem. And I solve this by replace space by " ". For example:
replace
python Application.py "cmd -option"
by
python Application.py "cmd -option"
.
Not sure for your problem.