'NoneType' object has no attribute 'print' error

Question

So for a task I need to be able to reflect the y-value of a tuple. This is what I have so far, but I keep getting this error: 'NoneType' object has no attribute 'print'

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def print(self):
        print((self.x, self.y))
    def reflect_x(self):
        if self.y < 0:
            print((self.x, abs(self.y)))
        if self.y > 0:
            print((self.x, -abs(self.y)))

if __name__ == "__main__":
    p1 = Point(1,4)
    p1.reflect_x().print()

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

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

These are the values I should be getting:

(1, -4)
(-3, -5)
(-3, 5)

The bottom part (in if __name__ == "__main__":) is a test code which I'm not allowed to change, so the main problems should be lying in the top part, so basically inside the Point-class.

Answer 1

The method reflect_x implicitly returns None. You have to either call the custom print method on the class object itself or return self in your reflect_x.

EDIT by call the custom print method on the class object itself I mean to change the last part of the code as follows

if __name__ == "__main__":
    p1 = Point(1,4)
    p1.reflect_x()
    p1.print()

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

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

which will work because the custom print method is a member of the Point class.

And the second option of returning self from the reflect_x method will work as well because we return the reference of the object instance. See this: https://www.online-python.com/hHg4Ya3yG7

These two points only focus on the aspect to resolve the 'NoneType' object has no attribute 'print' issue. To achieve the results we are looking for, modify the code like so:

def reflect_x(self):
    if self.y < 0:
        self.y = abs(self.y)
    elif self.y > 0:
        self.y = -abs(self.y)
    return self

which will print the desired result of

(1, -4)
(-3, -5)
(-3, 5)

Answer 2

Your method Point.reflect_x() doesn't have a return, so it returns None. You are trying to call the function print in Point.reflect_x(), wich is the source of your error.

To solve this, just call Point.print() instead of Point.reflect_x().print()

if __name__ == "__main__":
    p1 = Point(1,4)
    p1.reflect_x()
    p1.print()

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

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

Also, change your reflect_x method:

def reflect_x(self):
    self.y *= -1

Answer 3

Your reflect function doesn't change the class - it returns None, which doesn't have a print function, as the error says

To "reflect over the X-axis", you don't need absolute values, just multiply by negative one

Plus, adding a print method to the class is not Pythonistic. You should implement __str__

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

    def __str__(self):
        return f'({self.x},{self.y})'

    def reflect_x(self):
        self.y *= -1

Then you can do

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

If you need the exact code shown in the main execution part and can only change the class, then

change only

def reflect_x(self):
    self.y *= -1
    return self

Then this will work

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

Answer 4

reflect_x() should return a Point object.

def reflect_x(self):
    cls = type(self)
    return cls(self.x, -self.y)

It'd also be possible to modify self then return it, but conventionally, mutators return None in Python to avoid confusion.

By the way, this style facilitates method chaining, and it's commonly used in Pandas for example.

Answer 5

Remove the .print() after p1.reflect_x:

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
        
    def print(self):
        print(self.x, self.y)
        
    def reflect_x(self):
        if self.y < 0:
            print((self.x, abs(self.y)))
        if self.y > 0:
            print((self.x, -abs(self.y)))

if __name__ == "__main__":
    p1 = Point(1,4)
    p1.reflect_x()

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

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