I wrote out a test for a Complex class on python but I'm getting an error. Here's what I have:

```
class Complex:
def __init__(self, real=0, imaginary=0):
self._r=real
self._i=imaginary
def __add__ (self, other):
return Complex((self._r + other._r), (self._i + other._i))
def __sub__ (self, other):
return Complex((self._r - other._r), (self._i - other._i))
def __mul__ (self, other):
return Complex((self._r * other._r - self._i * other._i), (self._r * other._i + self._i * other._r))
def __truediv__ (self, other):
return Complex(((self._r * other._r + self._i * other._i)) / (self._i**2 + other._i**2), ((self._r * other._i - other._r * self._i)) / (self._i**2 + other._i**2))
def __str__ (self):
if self._i < 0:
return (str(self._r)+ "-" + str(-self._i) + "i")
else:
return (str(self._r) + "+" + str(self._i) + "i")
def test():
try:
while True:
R1 = float(input("Enter first real number: "))
I1 = float(input ("Enter first imaginary number: "))
f1 = (R1, I1)
print ("The first set of numbers are ", f1)
R2 = float(input("Enter second real number: "))
I2 = float(input("Enter second imaginary: "))
f2 = (R2,I2)
print ("The second set of numbers are ", f2)
print (f1, "+", f2, "=", f1.__add__ (f2))
print (f1, "-", f2, "=", f1.__sub__(f2))
print (f1, "*", f2, "=", f1.__mul__ (f2))
print (f1, "/", f2, "=", f1.__truediv__ (f2))
except ValueError:
pass
test()
```

I get error: AttributeError: 'tuple' object has no attribute '**sub**'

Why is this happening?