How to use *args in a python class?

Question

I am trying to get some args working in a class, I already got it running in a function from How to use *args in a function?.

I'm trying to get that function into a class but I don't seem to understand how to initialize that class which has an init function taking *args. The code is as following :

class classname(object):
    def __init__(self, *args):
        <code-snip>
        ...
        </code-snip>

if __name__ == "__main__":
    start = classname()
    start()

So here I'm confused on what to do with 'start()'. Do I have to use 'start(*sys.argv[1:])' or 'start()'. Both doesn't seem to work. I want to get the *args which is expected in init to be passed properly.

Any pointers please.

Thanks a ton..

======

I'm sorry if I wasn't clear on detailing how it didn't work.

a) While using start(*sys.argv[1:])

Traceback (most recent call last):
  File "check.py", line 126, in <module>
    start(*sys.argv[1:])
TypeError: 'check' object is not callable

b) While using start(), I get :

Traceback (most recent call last):
  File "check.py", line 126, in <module>
    start()
TypeError: 'check' object is not callable

These were the errors which came up.

@alko, yes you are correct. I was looking on how to get the *args in init passed properly.

read this question you understand the concept http://stackoverflow.com/questions/3394835/args-and-kwargs — MONTYHS, Nov 07 '13 at 08:27
@MONTYHS The irritation obviously comes from the uncertainty which methods are called when, and not from the `*, **` stuff itself. — glglgl, Nov 07 '13 at 08:29
If I got a dime whenever I read "It doesn't seem to work" without any further explanation, I'd be rich. — glglgl, Nov 07 '13 at 08:29
imho this is clearly stated as `I want to get the *args which is expected in init to be passed properly.` — alko, Nov 07 '13 at 08:37

score 8 · Answer 1 · edited Oct 11 '15 at 11:17

Objects are instantiated by passing arguments to class constructor. They are in turn initalized with __init__ function. In your example this would be

start = ClassName(*sys.argv[1:])

that expression is processed as follows:

New instance of classname is instantiated with object.__new__(ClassName, *sys.argv[1:]) named start in local namespace. From now on start object may be referenced inside your if __name__ == "__main__" script.
Its contents are in turn initialized invoking start.__init__(*sys.argv[1:]). Note that args to __init__ are the same passed to constructor.

And read PEP 8 for python naming convention. That is:

Class names should normally use the CapWords convention.

score 0 · Answer 2 · answered Nov 07 '13 at 08:27

Your example contains a class which is first instantiated - which involves calling __init__() - and then called - which is done by calling __call__().

So your stuff should be put in the call start = classname(...) in order to be passed to __init__().

The call to the newly instantiated object will fail, however, unless it contains a __call__() method. That would have been easier to answer if you had told us what

Both doesn't seem to work.

exactly means.

How to use *args in a python class?

2 Answers2