Reducing the number of parameters a function takes in python

Question

I have the following structure in my code:

#!/usr/bin/env python
import <something>
.
.
.
from modules import *
from optparse import OptionParser

class Main:
    def __init__(self):
        parser = self.get_argument()
        self.set_argument(parser)

    def my_args(self):
        parser = OptionParser(usage='usage: %prog [options]', version='%prog 1.0.0')
        parser.add_option('-t', '--test', action='store_true', dest='test', default=False,
            help='Help of test.')
        .
        .
        .
        return parser

    def set_args(self, parser)
        options, args = parser.parse_args()
        params = dict(test=options.test, ..., arg100=options.arg100)
        self.start(**params)

    def start(self, **params):
        print params


    def ...:
        ...
    .
    .
    .

if __name__ == '__main__':
    Main()

I want to run start for getting parameters and its values for using in other functions. but:

TypeError: start() takes exactly 2 arguments (1 given)

How can I use kwargs for passing them?

What is best way in order to use parameters in start. I am really new with kwargs.

How are you calling the start() method? If I use the start() method you've written above, it doesn't error, just prints out an empty dictionary. — Simon Fraser
– Simon Fraser, Commented Mar 9, 2016 at 8:25
pardon, yes. you are right. how can I use kwargs for passing them? — MLSC
– MLSC, Commented Mar 9, 2016 at 8:26
start is define to take kwargs or keyword arguments, because you put the ** in front of params, then in set_args you define params but you pass test, which is not even declared and you do not pass any keyword params. I don't know if you have another test declared somewhere. You might want to fix those problems. — Daniele Bernardini
– Daniele Bernardini, Commented Mar 9, 2016 at 8:26

Clément Schreiner · Accepted Answer · 2016-03-09 08:47:14Z

1

**kwargs allows a function to take keywords arguments, and constructs a dictionary

In [3]: def g(**kw):
...:     print(kw)
...:     

In [4]: g(a=1, b=2, c=3)
 {'a': 1, 'c': 3, 'b': 2}

If you want to pass a dictionary to the function, you'll need to unpack the dictionary, like this:

In [5]: d = dict(e=42, f=65)

In [6]: g(**d)
   {'e': 42, 'f': 65}

See http://pythontips.com/2013/08/04/args-and-kwargs-in-python-explained/, or the official documentation

edited Mar 9, 2016 at 8:47

answered Mar 9, 2016 at 8:27

Clément Schreiner

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3 Comments

MLSC Over a year ago

How this code can be changed and use kwargs for passing arguments?

MLSC Over a year ago

please see update, The error is TypeError: start() takes exactly 2 arguments (1 given) when I call self.start(**params)

Clément Schreiner Over a year ago

What happens when you print params before calling start?

Daniele Bernardini · Accepted Answer · 2016-03-09 08:44:54Z

0

The following works for me:

class Test(object):

    def a(self):
        p = {"a":1, "b":2}
        self.start(**p)

    def start(self, **params):
        print(params)


t = Test()
t.a()

result is:

{'a': 1, 'b': 2}

answered Mar 9, 2016 at 8:44

Daniele Bernardini

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