Operator Overloading in Python --- Currency class

Things to do.

• Create a class called Currency that takes rupee and paise as input and adjusts the values. 10 rupees and 250 paise should become 12 rupees and 50 paise
• Print the output in proper format. ₹ 01.12   
• Create a iterator that returns the rupee first and the paise next
• Create an indexed system that returns rupees at position 0 and paise at position 1.
• Overload the comparison operators.

"""
Starting a class that will be a complete example of Python OOPs
We will implement operator overloading as well.

The Currency class takes rupees and paise as input. Converts
paise >=100 into rupees and proceeds

"""
'''
Operators that can be overloaded

Operator. Required Method
+  __add__(self, other)
–  __sub__(self, other)
*  __mul__(self, other)
/  __truediv__(self, other)
// __floordiv__(self, other)
%  __mod__(self, other)
** __pow__(self, other)
>> __rshift__(self, other)
<< __lshift__(self, other)
&  __and__(self, other)
|  __or__(self, other)
^  __xor__(self, other)
Comparison Operators :
Operator   Methods
<  __lt__(self, other)
>  __gt__(self, other)
<= __le__(self, other)
>= __ge__(self, other)
== __eq__(self, other)
!= __ne__(self, other)
Assignment Operators :
Operator   Method to be overloaded
-= __isub__(self, other)
+= __iadd__(self, other)
*= __imul__(self, other)
/= __idiv__(self, other)
//=    __ifloordiv__(self, other)
%= __imod__(self, other)
**=    __ipow__(self, other)
>>=    __irshift__(self, other)
<<=    __ilshift__(self, other)
&= __iand__(self, other)
|= __ior__(self, other)
^= __ixor__(self, other)
Unary Operators :
Operator   Method to be overloaded
–  __neg__(self)
+  __pos__(self)
~  __invert__(self)
Note: It is not possible to change the number of operands of an operator. For ex. you cannot overload a unary operator as a binary operator. The following code will throw a syntax error.




'''


class Currency:  # Starting a class declaration
    def __next__(self):  # Returs rupees the first time and paise the next time
        n = self.counter
        self.counter += 1
        if self.counter > 2:
            raise StopIteration

        if n == 0:
            return self.pad0(self.total // 100)
        return self.pad0(self.total % 100)

    def __iter__(self):
        self.counter = 0
        return self

    def pad0(self, n):  # Add leading 0 to numbers less than 10
        if n < 10:
            return "0{0}".format(n)
        return "{0}".format(n)

    def __init__(self, rs, paise):  # Constructor. Converts rs and paise to a total in paise and stores
        self.total = rs * 100 + paise

    def __str__(self):  # str function converts total to rupee and paise
        r = self.total // 100
        p = self.total % 100
        r = self.pad0(r)
        p = self.pad0(p)
        return "₹ {0}.{1}".format(r, p)

    def __add__(self, other):  # Implements the + operator
        return Currency(0, self.total + other.total)

    def __gt__(self, other):  # Implements the > operator
        return self.total > other.total

    def __getitem__(self, item):
        if item == 0:
            return self.pad0(self.total // 100)
        if item == 1:
            return self.pad0(self.total % 100)
        raise IndexError("list index out of range")

    def __len__(self):  # This is for a loop through sequence.We have two items rupees and paise
        return 2


c1 = Currency(1, 12)
print("C1 ", c1)
for i in c1:
    print(i)
c2 = Currency(2, -90)
print("C2 ", c2)
print("0",c2[0])
print("1",c2[1])

Output

C1  ₹ 01.12
01
12
C2  ₹ 01.10
0 01
1 10

Process finished with exit code 0

Repo on GIT

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