integer +-* interval

[mcgrim]

this changed version of my previous code should be able to sum, subtract and multiply
an interval with an integer or float, and the result should be given by integers/floats
respectively.
for instance

1 + interval(2,3) should give [3,4]
but

1.0 + interval(2,3) should give [3.0, 4.0]

I thought that for addition, I had to use __radd__ and I am not sure if I am right.


This is the code:

class interval:
    def __init__(self,left,right):
        self.right=right
        self.left=left
    def __radd__(self,other):
        a,b = self.left + other, self.right + other
        return interval(a+b)
    
    def __sub__(self,other):
        a,b,c,d=self.left,self.right,other.left,other.right
        return interval(min(a,b)-max(c,d),max(a,b)-min(c,d))
    def __mul__(self,other):
        a,b,c,d=self.left,self.right,other.left,other.right
        return interval(min(a*c, a*d, b*c, b*d),
                            max(a*c, a*d, b*c, b*d))
    def __truediv__(self, other):
        a, b, c, d = self.left, self.right, other.left, other.right
        # [c,d] cannot contain zero:
        print(min(a/c, a/d, b/c, b/d))
        
        if c*d <= 0:
            raise ValueError ('Interval %s cannot be denominator because it contains zero' % other)
        
        return interval(min(a/c, a/d, b/c, b/d), max(a/c, a/d, b/c, b/d))
    
    def __contains__(self,other):
        return (other>=self.left and other<=self.right)
    
    def __repr__(self):
        return '[{},{}]'.format(self.left,self.right)


print(interval(1,2) + 1)

and this is the error I get:

Error:
  File "<ipython-input-838-717f169c285d>", line 1, in <module>
    runfile('C:/Users/Desktop/python ode/extrial.py', wdir='C:/Users/Desktop/python ode')

  File "C:\Users\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 668, in runfile
    execfile(filename, namespace)

  File "C:\Users\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 108, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "C:/Users/Desktop/python ode/extrial.py", line 221, in <module>
    print(interval(1,2) + 1)

TypeError: unsupported operand type(s) for +: 'interval' and 'int'

[Yoriz]

its not __radd__ its __add__ also return interval(a+b) should be return interval(a, b)

[mcgrim]

ok, I had __add__ before but didn't work either.
What should I change in my code to obtain I listed above?