Dunder Methods

__init__

• This method is implicitly called by the class and sets up all the attributes for us

__bases__

You have to remember that the __bases__ property holds the information about the immediate super class of the class. It is not aware of any other hierarchy. Also, it contains the super classes in a tuple and NOT a list.

class A:
	pass

class B(A):
	pass

class C(B):
	pass

print(C.__bases__)

- Output: (<class '__main__.B'>, )

__dict__

class A:
	var = 100
	def __init__(self):
		pass
	
a = A()
print(a.__dict__)

Every object in python has an attribute which is denoted by __dict__. And this object contains all attributes defined FOR the object. Since var has not been defined with the self keyword, it is a CLASS variable and will be shared by ALL objects of class A. Due to this it will not appear in the 'dict' property of object a. 'var' will be present in the 'dict' property of class A. So output for above code will be an empty dictionary.

__repr__

• Unambiguas representation of the object - Used for debugging and meant for devs

• Is good to implement this to return a string used to recreate the object:

• once you print the object, it should return how to re-create the object

print(emp_1)

__str__

• Readable version of the object

• is meant to be as a display for the end user

• Should return the username and email address when printed

print(emp_1)

Both these dunder methods are called directly from py:

• This outputs the same result as the above print statements

__add__

Integer:

• This is used for arihmetic

• The above code is basically the same thing

• In the second print statement is how python calls it

String:

• Strings use their special __add__ method

• This method will output: ab

By defining the __add__ dunder method you are able to add employee salaries for example:

__len__

• By using len(object) you are calling a dunder method in the backgroud: