Power a number with input() and function within class

Question

I'm able to calculate area of square without using class/method but when I want to add it to the class if it is failing on line 8 with the following error:

area() takes 1 positional argument but 2 were given

My code try is:

class Square():
    def area(side_length):
        calc = side_length**2
        return calc

figure = Square()
side_length = int(input("Enter side length: "))
print(figure.area(side_length))

If I run this code, it works fine. I think I'm doing smth wrong in calling methods:

def area(side_length):
        calc = side_length**2
        return calc
side_length = int(input("Enter side length: "))
area(side_length)

Also, `side_length` should probably be an attribute of the `Square`, passed into the constructor. Otherwise there is no point having a class. — Thomas, Aug 17 '22 at 10:34

score 2 · Answer 1 · edited Aug 21 '22 at 04:27

2

You're missing self:

class Square():
    def area(self, side_length):
        calc = side_length**2
        return calc

figure = Square()
side_length = int(input("Enter side length: "))
print(figure.area(side_length))

Remember, in Python OOP, every single function need to have self parameter.

edited Aug 21 '22 at 04:27

Jonathan Ciapetti

1,261
3
11
16

answered Aug 17 '22 at 10:43

2

While here `self` is necessary, there exist also static methods that although being part of a class, they don't need the `self` parameter. – Jonathan Ciapetti Aug 21 '22 at 02:41

score 1 · Answer 2 · answered Aug 17 '22 at 10:40

All class methods (which are not decorated with @staticmethod or @classmethod) need a self parameter:

class Square:
    def area(self, side_length):
        calc = side_length ** 2
        return calc

figure = Square()
side_length = int(input("Enter side length: "))
print(figure.area(side_length))

But, as mentioned in the comments by Thomas, there is no real point in having the class if you don't do something like this:

class Square:
    def __init__(self, side_length):
        self.side_length = side_length
    def area(self):
        calc = self.side_length ** 2
        return calc

side_length = int(input("Enter side length: "))
figure = Square(side_length)
print(figure.area())

MoRe · Accepted Answer · 2022-08-17T11:28:11.877

class Square():
    def area(self, side_length):
        calc = side_length**2
        return calc

figure = Square()
side_length = int(input("Enter side length: "))
print(figure.area(side_length))

please mind that in python, every instance method has at least one argument, for example there. when you call figure.area, you are passing two parameters to area method:

figure object (that is always first parameter)
side_length

so when you are defining an instance method, you must set a parameter for figure object even if you don't use it... It can have any name you want, but it is highly recommended to use self and it is a contract. self refers to figure

Thanks! Marking this answer as right one because of additional information provideed — Mamed, Aug 17 '22 at 11:22

score 0 · Answer 4 · answered Aug 17 '22 at 10:38

0

you forgot self parameter

class Square():
def area(self, side_length):
    calc = side_length**2
    return calc

figure = Square()
side_length = int(input("Enter side length: "))
print(figure.area(side_length))

answered Aug 17 '22 at 10:38

Omid

35
6

Power a number with input() and function within class

4 Answers4