I don't understand how python methods within a class work-CodePudding

So I'm new to programming and I'm trying to learn how to code in uni.

We just started learning classes in python and I can't solve this problem.

I need to create a method reflect-x so that the variable y is negative. Here is the code I wrote

class Point:
    def __init__(self,x,y):
        self.x=x
        self.y=y

    def reflect_x(self):
        if self.y < 0:
            self.y = self.y
        else:
            self.y = -abs(self.y)
    def print(self):
        a = self.x , self.y
        print(tuple(a))

And this is what the site uses to check if the code is correct


p1 = Point(1, 4)
p1.reflect_x().print()

p2 = Point(-3, 5)
p2.reflect_x().print()

p3 = Point(-3, -5)
p3.reflect_x().print()

I keep getting " AttributeError: 'NoneType' object has no attribute 'print' " , and I don't know what to do.

CodePudding user response：

Welcome to programming!

Your method defining reflect_x returns None, which doesn't have a member function print. What you want is reflect_x to return a Point instead:

class Point:                                                                                            
    def __init__(self,x,y):                                                                             
        self.x=x                                                                                        
        self.y=y                                                                                        
                                                                                                        
    def reflect_x(self):                                                                                
        return Point(self.x, -self.y)                                                                   
                                                                                                        
    def printout(self):                                                                                 
        a = self.x , self.y                                                                             
        print(tuple(a))                                                                                 
                                                                                                        
p1 = Point(1, 4)                                                                                        
p1.printout()                                                                                           
                                                                                                        
p2 = Point(-3, 5)                                                                                       
p2.reflect_x().printout()                                                                               
                                                                                                        
p3 = Point(-3, -5)                                                                                      
p3.printout()

Note I changed print=>printout. Don't use reserved keywords for names in your developing!!!

CodePudding user response：

You have to call two methods (reflect, print) separately.

But if you have instinct to do the in such way you can approach it like this

class Point:
    def __init__(self,x,y):
        self.x=x
        self.y=y

    def reflect_x(self):
        if self.y > 0:
            self.y = -abs(self.y)
        return self # Return self will give you the instance itself

    def print(self):
        a = self.x , self.y
        print(tuple(a))

p1 = Point(1, 4)
p1.reflect_x().print()

p2 = Point(-3, 5)
p2.reflect_x().print()

p3 = Point(-3, -5)
p3.reflect_x().print()