Passing arguments to a function in Python

Question

I'm not sure why I'm getting the message error

TypeError: __init__() takes exactly 3 arguments (4 given)

for the code described below:

class Worker(object):
    def __init__(arg1,arg2,arg3):
        self.arg1 = arg1
        self.arg2 = arg2
        self.arg3 = arg3
    def some_function(self):
        print "it works: " + arg1 + arg2 + arg3

w=Worker("a","b","c")
w.some_function()

What could I be missing?

Blair · Accepted Answer · 2012-10-12 11:05:01Z

6

It should be def __init__(self, arg1,arg2,arg3):. You'll also need to change the print statement in some_function to

print "it works: " + self.arg1 + self.arg2 + self.arg3

answered Oct 12, 2012 at 11:05

Blair

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clyfish · Accepted Answer · 2012-10-12 11:02:35Z

4

def __init__(self,arg1,arg2,arg3):

answered Oct 12, 2012 at 11:02

clyfish

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2 Comments

thclpr Over a year ago

after updating with your sugestion, im having: NameError: global name 'arg1' is not defined. should i set global arg1, arg2 , arg3 ?

thclpr Over a year ago

Ah, thanks, i figured that out after writing the comentary. thanks for that :)

TZHX · Accepted Answer · 2012-10-12 11:27:41Z

1

The first argument expected for any class function should always be self.

Well, the name is unimportant, but that's the meaning of it.

So your function definintion should look like:

def __init__(self,arg1,arg2,arg3): 
    self.arg1 = arg1 
    self.arg2 = arg2 
    self.arg3 = arg3

edited Oct 12, 2012 at 11:27

answered Oct 12, 2012 at 11:02

TZHX

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6 Comments

Markus Unterwaditzer Over a year ago

This is only true for the methods of instances of a class. Not if you use the methods directly on the class: Worker.some_function(self) is equivalent to w.some_function()

TZHX Over a year ago

@MarkusUnterwaditzer so the function shouldn't be defined as def __init__(self, arg1, arg2, arg3)??

Markus Unterwaditzer Over a year ago

They should. I'm just saying because you said it's true for all methods. There are also classmethods that don't take the self argument.

rantanplan Over a year ago

@MarkusUnterwaditzer class method is a confusing term also. Since there is a @classmethod decorator that passes the class as the first argument.

Markus Unterwaditzer Over a year ago

@rantanplan I just call them methods (the ones that take self as first arg) and class-methods (the ones using the @classmethod decorator).

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