class Fraction:

def __init__(self, top, bottom):
    self.top = top
    self.bottom = bottom

def __repr__(self):
    return f"{self.top}/{self.bottom}"

def __ne__(self, other):
    ne_first_top = self.top * other.bottom
    ne_second_top = self.bottom * other.top
    return ne_first_top != ne_second_top

def __eq__(self, other):

    first_top = self.top * other.bottom
    second_top = other.top * self.bottom

    return first_top == second_top

f1 = Fraction(2, 3)
f3 = Fraction(1, 4)
assert f1 != f3 == True

When I run this code, I get the error AttributeError: 'bool' object has no attribute 'bottom'. Can I run this code without changing last line?

CodePudding user response：

The last line is incorrect because f3 == True is being evaluated first. It'd work if you did:

assert (f1 != f3) == True

or more simply (because True == True is always True):

assert f1 != f3

Technically you could make it "work" by forcing f3 == True to return f3, so that f1 != (f3 == True) will actually do what you want it to do:

    def __eq__(self, other):
        if other == True:
            return self

but don't do that. It would be extremely silly.

Note that since you've defined __eq__, you don't need to explicitly define __ne__ as its opposite. If __ne__ isn't explicitly defined it will just automatically be interpreted as "not __eq__"; Python doesn't generally force you to do extra work if it can at all be avoided.

CodePudding user response：

If you want to compare objects of different classes, you could amend your eq() method to handle it gracefully. At its simplest, you can do:

def __eq__(self, other):

    if type(self) == type(other):
        first_top = self.top * other.bottom
        second_top = other.top * self.bottom
        return first_top == second_top
    else:
        return False

Of course, if you want Fraction(1,1) == True to return True, then you'll need to elaborate your __eq__() method a bit further.