python: too many parameters provided

Question

could anyone please explain what's wrong with it ? am I doing something wrong ?

>>> class qw: 
...     def f2x(par1, par2, par3): 
...             print par1, par2, par3 
...
>>> obj = qw()
>>> obj.f2x("123", 13, "wert") Traceback (most recent call last):  
File "<stdin>", line 1, in <module>
TypeError: f2x() takes exactly 3 arguments (4 given)
>>>

if I will define just a function it's all working fine

>>> def f2x(par1, par2, par3):
...     print par1, par2, par3
... 
>>> f2x("1", 2, "too many")
1 2 too many
>>>

Answer 1

You forgot that all member functions get another argument implicitly, which in Python is called self by convention.

Try:

class qw:
  def f2x(self, par1, par2, par3):
    print par1, par2, par3

But still call it as before:

obj = qw()
obj.f2x("123", 13, "wert")

In f2x, self is the object on which the member was called. This is a very fundamental concept of Python you should really learn about.

Answer 2

You need the self parameter in your class' instance method definition:

class qw:
    def f2x(self, par1, par2, par3):
        print par1, par2, par3

I'd suggest going through a beginner Python book/tutorial. The standard tutorial is good choice, especially if you already have some experience in another language.

Then you call it like so:

g = qw()
g.f2x('1', '2', '3')

Answer 3

I guess its because of every method of a python class object implicitly has a first paramter which points to the object itself.

try

def f2x(self, par1, par2, par3):

you still call it with your 3 custom parameters

>>> class qw:
...     def f2x(self, p1, p2, p3):
...             print p1,p2,p3
... 
>>> o = qw()
>>> o.f2x(1,2,3)
1 2 3