Dunder Methods

Ref https://holycoders.com/python-dunder-special-methods/
See the end of page for example

Dunder	Description
`__new__(self)`	return a new object (an instance of that class). It is called before init method. Know More
`__init__(self)`	is called when the object is initialized. It is the constructor of a class.
`__del__(self)`	for del() function. Called when the object is to be destroyed. Can be used to commit unsaved data or close connections.
`__repr__(self)`	for repr() function. It returns a string to print the object. Intended for developers to debug. Must be implemented in any class.
`__str__(self)`	for str() function. Return a string to print the object. Intended for users to see a pretty and useful output. If not implemented, repr will be used as a fallback.
`__bytes__(self)`	for bytes() function. Return a byte object which is the byte string representation of the object.
`__format__(self)`	for format() function. Evaluate formatted string literals like % for percentage format and ‘b’ for binary.
`__lt__(self, anotherObj)`	for < operator.
`__le__(self, anotherObj)`	for <= operator.
`__eq__(self, anotherObj)`	for == operator.
`__ne__(self, anotherObj)`	for != operator.
`__gt__(self, anotherObj)`	for > operator.
`__ge__(self, anotherObj)`	for >= operator.
`__hash__(self)`	for `hash(obj)`, it should return an integer. `obj1 == obj2` should mean `hash(obj1) == hash(obj2)`
`__bool__(self)`	for `bool(obj)`, if not defined, then `__len__` is called and obj is defined as true if `__len__` returns non 0

Arithematic¶

Dunder	Description
`__add__(self, y)` `__sub__(self, y)` `__mul__(self, y)`	for +, -, * operation on object.
`__and__(self, y)` `__or__(self, y)` `__xor__(self, y)` `__neg__(self)`	obj & y obj \| y obj ^ y negation of object
`__matmul__(self, y)`	for @ operator (numpy matrix multiplication).
`__truediv__(self, y)`	for simple / division operation on object.
`__floordiv__(self, y)`	for // floor division operation on object.
`__mod__(self, y)`	obj % anotherobj
`__pow__(self, y)`	obj ** y
`__lshift__(self, y)`	obj << y
`__abs__(self)`	make support for abs() function. Return absolute value.
`__round__(self, nDigits)`	for round() function. Round off float type to 2 digits and return it.
`__int__(self)` `__float__(self)` `__complex__(self)`	support for int(), float() and complex() methods on object
`__trunc__(self)`	for trunc() function of math module. Returns the real value of the object.
`__ceil__(self)` `__floor__(self)`	for ceil() and floor() function on object.

Containor type¶

Dunder	Description
`__len__(self)`	for len() function. Returns the total number in any container.
`__getitem__(self, key)`	to support indexing. LIke container`[index]` calls container.__getitem(key)explicitly.
`__setitem__(self, key, value)`	makes item mutable (items can be changed by index), like container`[index]` = otherElement.
`__delitem__(self, key)`	for del() function. Delete the value at the index key.
`__iter__(self)`	returns an iterator when required that iterates all values in the container.
`__dir__(self)`	A sequence must be returned
`__contains__(self, x)`	Should returns the output of `x in obj`

class Account:
    # def __new__(self):
    #     print("__new__ called A new account is Created.")
    def __init__(self, name, balance = 0):
        self.name = name
        self._balance = balance
        print("(__init__) Account Created with {} balance".format(self._balance))
    def getBalance(self):
        return self._balance
    def __repr__(self):
        return "(__repr__) Account({0}, {1})".format(self.name, self._balance)
    def __str__(self):
        return "(__str__) Account Name = {0}, Account Balance = {1}".format(self.name, self._balance)
    def __lt__(self, otherObj):
        try:
            return self._balance<otherObj.getBalance()
        except:
            return "Cannot Be compared."
    def __del__(self):
        self._balance = 0
        print("(__del__) Account Deleted")

digvijay_ac = Account("Digvijay Singh", 500)
saket_ac = Account("Digvijay Singh", 700)

print(str(digvijay_ac))
print(repr(digvijay_ac))
print(digvijay_ac<saket_ac)

OP:¶

(__init__) Account Created with 500 balance
(__init__) Account Created with 700 balance
(__str__) Account Name = Digvijay Singh, Account Balance = 500
(__repr__) Account(Digvijay Singh, 500)
True
(__del__) Account Deleted
(__del__) Account Deleted