Q:

Why does my use of click.argument produce "got an unexpected keyword argument 'help'? 

Running the following code results in this error:

TypeError: init() got an unexpected keyword argument 'help'

Code:
import click

@click.command()
@click.argument('command', required=1, help="start|stop|restart")
@click.option('--debug/--no-debug', default=False, help="Run in foreground")
def main(command, debug):
    print (command)
    print (debug)

if __name__ == '__main__':
    main()

Full error output:
$ python3 foo.py start
Traceback (most recent call last):
  File "foo.py", line 5, in <module>
    @click.option('--debug/--no-debug', default=False, help="Run in foreground")
  File "/home/cbetti/python/lib/python3/dist-packages/click-4.0-py3.4.egg/click/decorators.py", line 148, in decorator
    _param_memo(f, ArgumentClass(param_decls, **attrs))
  File "/home/cbetti/python/lib/python3/dist-packages/click-4.0-py3.4.egg/click/core.py", line 1618, in __init__
    Parameter.__init__(self, param_decls, required=required, **attrs)
TypeError: __init__() got an unexpected keyword argument 'help'

Why does this error occur? 

A:

I run into this again and again because the trace output does not correspond to the parameter causing the error.  Notice ArgumentClass in the trace, that's your hint. 
'help' is an acceptable parameter to @click.option.  The click library prefers, however, that you document your own arguments.  The @click.argument help parameter is causing this exception. 
This code works: (notice the lack of , help="start|stop|restart" in @click.argument)
import click

@click.command()
@click.argument('command', required=1)
@click.option('--debug/--no-debug', default=False, help="Run in foreground")
def main(command, debug):
    """ COMMAND: start|stop|restart """
    print (command)
    print (debug)

if __name__ == '__main__':
        main()

Output:
$ python3 foo.py start
start
False

Help Output:
Usage: test.py [OPTIONS] COMMAND

  COMMAND: start|stop|restart

Options:
  --debug / --no-debug  Run in foreground
  --help                Show this message and exit. 

A:

You are defining commands as arguments.  Note that click has a better way to define commands then what you are trying here. 
@click.group()
def main():
    pass

@click.command()
def start():
    print "running command `start`"

@click.command()
def stop():
    print "running command `stop`"

main.add_command(start)
main.add_command(stop)

if __name__ == '__main__':
    main()

will result in the following default help text:
Usage: test.py [OPTIONS] COMMAND [ARGS]...

Options:
  --help  Show this message and exit. 

Commands:
  start
  stop

Having said that, should you really need arguments, you cannot use the help parameter.  The click documentation indeed states that you should document your own arguments.  However, I have no idea how to do that.  Any hints? 

A:

click library does not allow -help parameter inside click.arguments (including the current version 6.7 when this comment has been written). 
But, you can use the -help parameter inside click.options. 
You can check current click documentation at http://click.pocoo.org/6/documentation/ or previous at http://click.pocoo.org/5/documentation/ this behaviour has not change recently. 
Then, it is a WAD.  It is not a BUG.