Optparse of python

Question

I am new to optparse of python and tried the following:

def plot():
    x=[1,2,3]
    y=[4,5,6]
    plt.plot(x,y)
    plt.savefig('trial.pdf')

parser=OptionParser()
parser.add_option("-p", "--plot", action="callback", callback=plot)
(options, args)=parser.parse_args()

I typed python3 parse.py -p in the terminal and it gave:

Traceback (most recent call last):
  File "firstparse.py", line 15, in <module>
    (options, args)=parser.parse_args()
  File "/usr/lib/python3.5/optparse.py", line 1386, in parse_args
    stop = self._process_args(largs, rargs, values)
  File "/usr/lib/python3.5/optparse.py", line 1430, in _process_args
    self._process_short_opts(rargs, values)
  File "/usr/lib/python3.5/optparse.py", line 1535, in _process_short_opts
    option.process(opt, value, values, self)
  File "/usr/lib/python3.5/optparse.py", line 784, in process
    self.action, self.dest, opt, value, values, parser)
  File "/usr/lib/python3.5/optparse.py", line 804, in take_action
    self.callback(self, opt, value, parser, *args, **kwargs)
TypeError: plot() takes 0 positional arguments but 4 were given

I do not understand well about the positional arguments error. Could anyone tell me where I wrong?

Answer 1

Check out the documentation:

When using callback, you supply a function that is used to process the incoming argument, this function is called with four arguments: option, opt_str, value, parser

option

is the Option instance that’s calling the callback

opt_str

is the option string seen on the command-line that’s triggering the callback...

value

is the argument to this option seen on the command-line...

parser

is the OptionParser instance driving the whole thing, mainly useful because you can access some other interesting data through its instance attributes...

Essentially you are trying to process the argument from command line into its value by processing it through plot function.

I suspect you are trying to choose, action (such a plot) to run from the command line, so perhaps more like:

parser=ArgumentParser()
parser.add_argument("-p", "--plot", action="store_true")
args = parser.parse_args()
if args.plot is True:
    plot()

Note: optparse has been deprecated since 3.2, you should nowadays be using argparse.