nargs=* equivalent for options in Click
Is there an equivalent to argparse's nargs='*' functionality for optional arguments in Click?
I am writing a command line script, and one of the options needs to be able to take an unlimited number of arguments, like:
foo --users alice bob charlie --bar baz
So users would be ['alice', 'bob', 'charlie'] and bar would be 'baz'.
In argparse, I can specify multiple optional arguments to collect all of the arguments that follow them by setting nargs='*'.
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--users', nargs='*')
>>> parser.add_argument('--bar')
>>> parser.parse_args('--users alice bob charlie --bar baz'.split())
Namespace(bar='baz', users=['alice', 'bob', 'charlie'])
I know Click allows you to specify an argument to accept unlimited inputs by setting nargs=-1, but when I try to set an optional argument's nargs to -1, I get:
TypeError: Options cannot have nargs < 0
Is there a way to make Click accept an unspecified number of arguments for an option?
Update:
I need to be able to specify options after the option that takes unlimited arguments.
Update:
@Stephen Rauch's answer answers this question. However, I don't recommend using the approach I ask for here. My feature request is intentionally not implemented in Click, since it can result in unexpected behaviors. Click's recommended approach is to use multiple=True:
@click.option('-u', '--user', 'users', multiple=True)
And in the command line, it will look like:
foo -u alice -u bob -u charlie --bar baz
One way to approach what you are after is to inherit from click.Option, and customize the parser.
Custom Class:
import click
class OptionEatAll(click.Option):
def __init__(self, *args, **kwargs):
self.save_other_options = kwargs.pop('save_other_options', True)
nargs = kwargs.pop('nargs', -1)
assert nargs == -1, 'nargs, if set, must be -1 not {}'.format(nargs)
super(OptionEatAll, self).__init__(*args, **kwargs)
self._previous_parser_process = None
self._eat_all_parser = None
def add_to_parser(self, parser, ctx):
def parser_process(value, state):
# method to hook to the parser.process
done = False
value = [value]
if self.save_other_options:
# grab everything up to the next option
while state.rargs and not done:
for prefix in self._eat_all_parser.prefixes:
if state.rargs[0].startswith(prefix):
done = True
if not done:
value.append(state.rargs.pop(0))
else:
# grab everything remaining
value += state.rargs
state.rargs[:] = []
value = tuple(value)
# call the actual process
self._previous_parser_process(value, state)
retval = super(OptionEatAll, self).add_to_parser(parser, ctx)
for name in self.opts:
our_parser = parser._long_opt.get(name) or parser._short_opt.get(name)
if our_parser:
self._eat_all_parser = our_parser
self._previous_parser_process = our_parser.process
our_parser.process = parser_process
break
return retval
Using Custom Class:
To use the custom class, pass the cls parameter to @click.option() decorator like:
@click.option("--an_option", cls=OptionEatAll)
or if it is desired that the option will eat the entire rest of the command line, not respecting other options:
@click.option("--an_option", cls=OptionEatAll, save_other_options=False)
How does this work?
This works because click is a well designed OO framework. The @click.option() decorator usually instantiates a
click.Option object but allows this behavior to be over ridden with the cls parameter. So it is a relatively
easy matter to inherit from click.Option in our own class and over ride the desired methods.
In this case we over ride click.Option.add_to_parser() and the monkey patch the parser so that we can
eat more than one token if desired.
Test Code:
@click.command()
@click.option('-g', 'greedy', cls=OptionEatAll, save_other_options=False)
@click.option('--polite', cls=OptionEatAll)
@click.option('--other')
def foo(polite, greedy, other):
click.echo('greedy: {}'.format(greedy))
click.echo('polite: {}'.format(polite))
click.echo('other: {}'.format(other))
if __name__ == "__main__":
commands = (
'-g a b --polite x',
'-g a --polite x y --other o',
'--polite x y --other o',
'--polite x -g a b c --other o',
'--polite x --other o -g a b c',
'-g a b c',
'-g a',
'-g',
'extra',
'--help',
)
import sys, time
time.sleep(1)
print('Click Version: {}'.format(click.__version__))
print('Python Version: {}'.format(sys.version))
for cmd in commands:
try:
time.sleep(0.1)
print('-----------')
print('> ' + cmd)
time.sleep(0.1)
foo(cmd.split())
except BaseException as exc:
if str(exc) != '0' and \
not isinstance(exc, (click.ClickException, SystemExit)):
raise
Test Results:
Click Version: 6.7
Python Version: 3.6.3 (v3.6.3:2c5fed8, Oct 3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)]
-----------
> -g a b --polite x
greedy: ('a', 'b', '--polite', 'x')
polite: None
other: None
-----------
> -g a --polite x y --other o
greedy: ('a', '--polite', 'x', 'y', '--other', 'o')
polite: None
other: None
-----------
> --polite x y --other o
greedy: None
polite: ('x', 'y')
other: o
-----------
> --polite x -g a b c --other o
greedy: ('a', 'b', 'c', '--other', 'o')
polite: ('x',)
other: None
-----------
> --polite x --other o -g a b c
greedy: ('a', 'b', 'c')
polite: ('x',)
other: o
-----------
> -g a b c
greedy: ('a', 'b', 'c')
polite: None
other: None
-----------
> -g a
greedy: ('a',)
polite: None
other: None
-----------
> -g
Error: -g option requires an argument
-----------
> extra
Usage: test.py [OPTIONS]
Error: Got unexpected extra argument (extra)
-----------
> --help
Usage: test.py [OPTIONS]
Options:
-g TEXT
--polite TEXT
--other TEXT
--help Show this message and exit.
You can use this trick.
import click
@click.command()
@click.option('--users', nargs=0, required=True)
@click.argument('users', nargs=-1)
@click.option('--bar')
def fancy_command(users, bar):
users_str = ', '.join(users)
print('Users: {}. Bar: {}'.format(users_str, bar))
if __name__ == '__main__':
fancy_command()
Add fake option with a needed name and none arguments nargs=0, then add 'argument' with the unlimited args nargs=-1.
$ python foo --users alice bob charlie --bar baz
Users: alice, bob, charlie. Bar: baz
But be careful with the further options:
$ python foo --users alice bob charlie --bar baz faz
Users: alice, bob, charlie, faz. Bar: baz
I ran into the same issue. Instead of implementing a single command line option with n number of arguments, I decided to use multiple of the same command line option and just letting Click make a tuple out of the arguments under the hood. I ultimately figured if Click didn't support it, that decision was probably made for a good reason.
https://click.palletsprojects.com/en/7.x/options/#multiple-options
here is an example of what I am saying:
instead of passing a single string argument a splitting on a delimiter:
commit -m foo:bar:baz
I opted to use this:
commit -m foo -m bar -m baz
here is the source code:
@click.command()
@click.option('--message', '-m', multiple=True)
def commit(message):
click.echo('\n'.join(message))
This is more to type, but I do think it makes the CLI more user friendly and robust.