Python - how do I return an int in string form?

Question

So for a point class I'm writing, I need to write a method that rounds and converts to an int in string form. This is what I did:

def __str__(self):
    return int(round(self.x))

So it rounds and converts to an int but it isn't in string form. I've tried using str but that doesn't work at all. So how can I get that to string form? Here's my entire point class:

import math


class Error(Exception):
    def __init__(self, message):
        self.message = message


class Point:

    def __init__(self, x, y):
        if not isinstance(x, float):
            raise Error ("Parameter \"x\" illegal.")  
        self.x = x
        if not isinstance(y, float):
            raise Error ("Parameter \"y\" illegal.")
        self.y = y


    def rotate(self, a):
        if not isinstance(a, float):
            raise Error("Parameter \"a\" illegal.")
        self.x0 = math.cos(a) * self.x - math.sin(a) * self.y
        self.y0 = math.sin(a) * self.x + math.cos(a) * self.y


    def scale(self, f):
        if not isinstance(f, float):
            raise Error("Parameter \"f\" illegal.")
        self.x0 = f * self.x
        self.y0 = f * self.y


    def translate(self, delta_x, delta_y):
        if not isinstance(delta_x, float):
            raise Error ("Parameter \"delta_x\" illegal.")
        self.x0 = self.x + delta_x
        if not isinstance(delta_y, float):
            raise Error ("Parameter \"delta_y\" illegal.")
        self.y0 = self.y + delta_y


    def __str__(self):
        return str(int(round(self.x)))
        return str(int(round(self.y)))

Now I also have a line class that I haven't finished writing yet so if this class looks fine then the error must be in my line class.

It's a weird error. The error says TypeError: str returned non-string (type NoneType). Is it possible that my str method is correct and the error is from somewhere else? — John Kyle
– John Kyle, Commented Mar 6, 2016 at 18:13
And yes I did use str without converting to an int first and it still gives me that exact error. — John Kyle
– John Kyle, Commented Mar 6, 2016 at 18:15
might be just the self.x is None at the time you print then, have you checked? — Mixone
– Mixone, Commented Mar 6, 2016 at 18:18
also, have you defined the __repr__ method? it might be what is causing the error — Mixone
– Mixone, Commented Mar 6, 2016 at 18:22

Sci Prog · Accepted Answer · 2016-03-06 18:13:17Z

3

class X:
  def __init__(self):
    self.x = 3.1415
  def __str__(self):
    return str(int(round(self.x)))

x = X()
print x

This does print 3

edited Mar 6, 2016 at 18:13

answered Mar 6, 2016 at 18:07

Sci Prog

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2 Comments

Mixone Over a year ago

he says at the end that he used str() though

Mixone Over a year ago

or do you think he might have tried str(round(self.x)) instead ?

jaqHollow · Accepted Answer · 2016-03-06 18:42:46Z

1

Just cast the value you return into string. In the Python data model,

object.__str__(self)

Called by str(object) and the built-in functions format() and print() to compute the “informal” or nicely printable string representation of an object. The return value must be a string object.

From Python Data Model

The __str__ function is a built in function that must return a informal string representation for the object. You are returning an Integer representation.

So just change your return to str(int(round(self.x)))

answered Mar 6, 2016 at 18:42

jaqHollow

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