The document discusses constructors and variables in object-oriented programming. It defines constructors as special methods that initialize instance variables during object creation. Constructors can be parameterized or non-parameterized. The document also distinguishes between class/static variables that are shared among all objects, instance/non-static variables that are unique to each object, global variables declared outside functions, and local variables declared inside functions. It provides examples of using constructors and different variable types in Python classes.

1. Constructor
1
A constructor is a special kind of method which is used for initializing the
instance variables during object creation.
Constructor is used for initializing the instance members when we create the
object of a class.
Constructors can be of two types.
Parameterized Constructor
Non-parameterized Constructor
Syntax:
def __init__(self):
#now all about the constructor

2. Default Constructor
2
class DemoClass:
num = 101
def read_number(self):
print(self.num)
obj = DemoClass()
obj.read_number()
Output:
101

3. Constructor without Parameter
3
class DemoClass:
num = 101
def __init__(self):
self.num = 999
def read_number(self):
print(self.num)
obj = DemoClass()
obj.read_number()
Output:
999

4. Constructor
4
class DemoClass:
num = 101
def __init__(self, data):
self.num = data
def read_number(self):
print(self.num)
obj = DemoClass(55)
obj.read_number()
obj2 = DemoClass(66)
obj2.read_number()
Output:
55

5. Constructor
5
class Addition:
num1=1000
num2=2000
num3=3000
def result(self):
self.num=self.num1+self.num2+self.num3
print('Output:',self.num)
Sum = Addition()
Sum.result()

6. Constructor
6
class Addition:
def __init__(self):
self.num1=1000
self.num2=2000
self.num3=3000
def result(self):
self.num=self.num1+self.num2+self.num3
print('Output:',self.num)
Sum = Addition()
Sum.result()

7. Constructor
7
class Person:
name = ""
age = 0
def __init__(self, personName, personAge):
self.name = personName
self.age = personAge
def showName(self):
print(self.name)
def showAge(self):
print(self.age)
person1 = Person("Richard", 23)
person2 = Person("Anne", 30)
person1.showAge()
person2.showName()

8. Variables
8
•Class or Static Variables
•shared by all objects
•Instance or non-static
•every object has a copy of it
•Global
• variable declared outside of the function or in
global scope is known as global variable.
•Local Variables
•variable declared inside the function's body or
in the local scope is known as local variable.

9. Class /static and instance/non static variables
9
class College:
branch = 'cse' # Class Variable
year = 2 # Class Variable
def __init__(self,name,roll):
self.name = name # Instance Variable
self.roll = roll # Instance Variable
a = College('abc', 1)
b = College('xyz', 2)
print(a.branch)
print(b.branch)
print(a.year)
print(b.year)
print(a.name)
print(b.name)
print(a.roll)
print(b.roll)

10. Global and local variables
10
def f():
print(s)
# Global scope
s = “It is better to fail in originality than to succeed in imitation"
f()
Output
It is better to fail in originality than to succeed in imitation

11. Global and local variables
11
def f():
s = "Stop chasing the money and start chasing the passion."
print(s)
# Global scope
s = "The way to get started is to quit talking and begin doing"
f()
print(s)
Output
Stop chasing the money and start chasing the passion
The way to get started is to quit talking and begin doing

12. Global and local variables
12
def f():
print(s)
s = "Stop chasing the money and start chasing the passion."
print(s)
# Global scope
s = "The way to get started is to quit talking and begin doing"
f()
print(s)
undefined: Error: local variable 's' referenced before assignment

13. Global and local variables
13
def f():
global s
print(s)
s = “I love programming"
print(s)
# Global Scope
s = "Python is great!"
f()
print(s)
Output
Python is great!
I love programming
I love programming

14. Global and local variables
14
def f():
y = "local"
f()
print(y)
NameError: name 'y' is not defined

15. Global and local variables
15
def f():
y = "local"
print(y)
f()
Output
local

16. Global and local variables
16
x = "global"
def f():
global x
y = "local"
x = x * 2
print(x)
print(y)
f()
Output
global global
local

17. Global and local variables
17
x = 5
def f():
x = 10
print("local x:", x)
f()
print("global x:", x)
Output
local x 10
global x 5