I would like to use argparse to parse boolean command-line arguments written as "--foo True" or "--foo False". For example:
my_program --my_boolean_flag False
However, the following test code does not do what I would like:
import argparse
parser = argparse.ArgumentParser(description="My parser")
parser.add_argument("--my_bool", type=bool)
cmd_line = ["--my_bool", "False"]
parsed_args = parser.parse(cmd_line)
Sadly, parsed_args.my_bool evaluates to True. This is the case even when I change cmd_line to be ["--my_bool", ""], which is surprising, since bool("") evalutates to False.
How can I get argparse to parse "False", "F", and their lower-case variants to be False?
This question is related to
python
boolean
argparse
command-line-arguments
A simpler way would be to use as below.
parser.add_argument('--feature', type=lambda s: s.lower() in ['true', 't', 'yes', '1'])
Simplest. It's not flexible, but I prefer simplicity.
parser.add_argument('--boolean_flag',
help='This is a boolean flag.',
type=eval,
choices=[True, False],
default='True')
EDIT: If you don't trust the input, don't use eval.
I think the most canonical way will be:
parser.add_argument('--ensure', nargs='*', default=None)
ENSURE = config.ensure is None
This works for everything I expect it to:
add_boolean_argument(parser, 'foo', default=True)
parser.parse_args([]) # Whatever the default was
parser.parse_args(['--foo']) # True
parser.parse_args(['--nofoo']) # False
parser.parse_args(['--foo=true']) # True
parser.parse_args(['--foo=false']) # False
parser.parse_args(['--foo', '--nofoo']) # Error
The code:
def _str_to_bool(s):
"""Convert string to bool (in argparse context)."""
if s.lower() not in ['true', 'false']:
raise ValueError('Need bool; got %r' % s)
return {'true': True, 'false': False}[s.lower()]
def add_boolean_argument(parser, name, default=False):
"""Add a boolean argument to an ArgumentParser instance."""
group = parser.add_mutually_exclusive_group()
group.add_argument(
'--' + name, nargs='?', default=default, const=True, type=_str_to_bool)
group.add_argument('--no' + name, dest=name, action='store_false')
oneliner:
parser.add_argument('--is_debug', default=False, type=lambda x: (str(x).lower() == 'true'))
I think a more canonical way to do this is via:
command --feature
and
command --no-feature
argparse supports this version nicely:
parser.add_argument('--feature', dest='feature', action='store_true')
parser.add_argument('--no-feature', dest='feature', action='store_false')
parser.set_defaults(feature=True)
Of course, if you really want the --arg <True|False> version, you could pass ast.literal_eval as the "type", or a user defined function ...
def t_or_f(arg):
ua = str(arg).upper()
if 'TRUE'.startswith(ua):
return True
elif 'FALSE'.startswith(ua):
return False
else:
pass #error condition maybe?
Similar to @Akash but here is another approach that I've used. It uses str than lambda because python lambda always gives me an alien-feelings.
import argparse
from distutils.util import strtobool
parser = argparse.ArgumentParser()
parser.add_argument("--my_bool", type=str, default="False")
args = parser.parse_args()
if bool(strtobool(args.my_bool)) is True:
print("OK")
Simplest way would be to use choices:
parser = argparse.ArgumentParser()
parser.add_argument('--my-flag',choices=('True','False'))
args = parser.parse_args()
flag = args.my_flag == 'True'
print(flag)
Not passing --my-flag evaluates to False. The required=True option could be added if you always want the user to explicitly specify a choice.
In addition to what @mgilson said, it should be noted that there's also a ArgumentParser.add_mutually_exclusive_group(required=False) method that would make it trivial to enforce that --flag and --no-flag aren't used at the same time.
class FlagAction(argparse.Action):
# From http://bugs.python.org/issue8538
def __init__(self, option_strings, dest, default=None,
required=False, help=None, metavar=None,
positive_prefixes=['--'], negative_prefixes=['--no-']):
self.positive_strings = set()
self.negative_strings = set()
for string in option_strings:
assert re.match(r'--[A-z]+', string)
suffix = string[2:]
for positive_prefix in positive_prefixes:
self.positive_strings.add(positive_prefix + suffix)
for negative_prefix in negative_prefixes:
self.negative_strings.add(negative_prefix + suffix)
strings = list(self.positive_strings | self.negative_strings)
super(FlagAction, self).__init__(option_strings=strings, dest=dest,
nargs=0, const=None, default=default, type=bool, choices=None,
required=required, help=help, metavar=metavar)
def __call__(self, parser, namespace, values, option_string=None):
if option_string in self.positive_strings:
setattr(namespace, self.dest, True)
else:
setattr(namespace, self.dest, False)
just do the following , you can make --test = True by using
python filename --test
parser.add_argument("--test" , default=False ,help="test ?", dest='test', action='store_true')
Quick and easy, but only for arguments 0 or 1:
parser.add_argument("mybool", default=True,type=lambda x: bool(int(x)))
myargs=parser.parse_args()
print(myargs.mybool)
The output will be "False" after calling from terminal:
python myscript.py 0
There seems to be some confusion as to what type=bool and type='bool' might mean. Should one (or both) mean 'run the function bool(), or 'return a boolean'? As it stands type='bool' means nothing. add_argument gives a 'bool' is not callable error, same as if you used type='foobar', or type='int'.
But argparse does have registry that lets you define keywords like this. It is mostly used for action, e.g. `action='store_true'. You can see the registered keywords with:
parser._registries
which displays a dictionary
{'action': {None: argparse._StoreAction,
'append': argparse._AppendAction,
'append_const': argparse._AppendConstAction,
...
'type': {None: <function argparse.identity>}}
There are lots of actions defined, but only one type, the default one, argparse.identity.
This code defines a 'bool' keyword:
def str2bool(v):
#susendberg's function
return v.lower() in ("yes", "true", "t", "1")
p = argparse.ArgumentParser()
p.register('type','bool',str2bool) # add type keyword to registries
p.add_argument('-b',type='bool') # do not use 'type=bool'
# p.add_argument('-b',type=str2bool) # works just as well
p.parse_args('-b false'.split())
Namespace(b=False)
parser.register() is not documented, but also not hidden. For the most part the programmer does not need to know about it because type and action take function and class values. There are lots of stackoverflow examples of defining custom values for both.
In case it isn't obvious from the previous discussion, bool() does not mean 'parse a string'. From the Python documentation:
bool(x): Convert a value to a Boolean, using the standard truth testing procedure.
Contrast this with
int(x): Convert a number or string x to an integer.
--feature and --no-feature at the same time (last one wins)This allows users to make a shell alias with --feature, and overriding it with --no-feature.
parser.add_argument('--feature', default=True, action=argparse.BooleanOptionalAction)
I recommend mgilson's answer:
parser.add_argument('--feature', dest='feature', action='store_true')
parser.add_argument('--no-feature', dest='feature', action='store_false')
parser.set_defaults(feature=True)
--feature and --no-feature at the same timeYou can use a mutually exclusive group:
feature_parser = parser.add_mutually_exclusive_group(required=False)
feature_parser.add_argument('--feature', dest='feature', action='store_true')
feature_parser.add_argument('--no-feature', dest='feature', action='store_false')
parser.set_defaults(feature=True)
You can use this helper if you are going to set many of them:
def add_bool_arg(parser, name, default=False):
group = parser.add_mutually_exclusive_group(required=False)
group.add_argument('--' + name, dest=name, action='store_true')
group.add_argument('--no-' + name, dest=name, action='store_false')
parser.set_defaults(**{name:default})
add_bool_arg(parser, 'useful-feature')
add_bool_arg(parser, 'even-more-useful-feature')
Here is another variation without extra row/s to set default values. The boolean value is always assigned, so that it can be used in logical statements without checking beforehand:
import argparse
parser = argparse.ArgumentParser(description="Parse bool")
parser.add_argument("--do-something", default=False, action="store_true",
help="Flag to do something")
args = parser.parse_args()
if args.do_something:
print("Do something")
else:
print("Don't do something")
print(f"Check that args.do_something={args.do_something} is always a bool.")
I was looking for the same issue, and imho the pretty solution is :
def str2bool(v):
return v.lower() in ("yes", "true", "t", "1")
and using that to parse the string to boolean as suggested above.
Simplest & most correct way is:
from distutils.util import strtobool
parser.add_argument('--feature', dest='feature',
type=lambda x: bool(strtobool(x)))
Do note that True values are y, yes, t, true, on and 1; false values are n, no, f, false, off and 0. Raises ValueError if val is anything else.
A quite similar way is to use:
feature.add_argument('--feature',action='store_true')
and if you set the argument --feature in your command
command --feature
the argument will be True, if you do not set type --feature the arguments default is always False!
As an improvement to @Akash Desarda 's answer, you could do
import argparse
from distutils.util import strtobool
parser = argparse.ArgumentParser()
parser.add_argument("--foo",
type=lambda x:bool(strtobool(x)),
nargs='?', const=True, default=False)
args = parser.parse_args()
print(args.foo)
And it supports python test.py --foo
(base) [costa@costa-pc code]$ python test.py
False
(base) [costa@costa-pc code]$ python test.py --foo
True
(base) [costa@costa-pc code]$ python test.py --foo True
True
(base) [costa@costa-pc code]$ python test.py --foo False
False
Convert the value:
def __arg_to_bool__(arg):
"""__arg_to_bool__
Convert string / int arg to bool
:param arg: argument to be converted
:type arg: str or int
:return: converted arg
:rtype: bool
"""
str_true_values = (
'1',
'ENABLED',
'ON',
'TRUE',
'YES',
)
str_false_values = (
'0',
'DISABLED',
'OFF',
'FALSE',
'NO',
)
if isinstance(arg, str):
arg = arg.upper()
if arg in str_true_values:
return True
elif arg in str_false_values:
return False
if isinstance(arg, int):
if arg == 1:
return True
elif arg == 0:
return False
if isinstance(arg, bool):
return arg
# if any other value not covered above, consider argument as False
# or you could just raise and error
return False
[...]
args = ap.parse_args()
my_arg = options.my_arg
my_arg = __arg_to_bool__(my_arg)
Source: Stackoverflow.com