Python

Python is an object oriented language.You can create class and their objects in Python.You can write OOP using Python but it is not necessary.In fact for for simple programs you will just write functions.
You define a class in Python using the class keyword followed by the name of the class.Once you have created a class you can create new objects of that class.The objects of the class consists of
attributes and fucntions defined by that class.

To define a new class implement the following steps:

1. declare a class header by specifying class name after the class keyword followed by colon(:) as:

class Employee:

define function within class as:
class Employee:
def fetchEmpDetails(self):
print("employee name")

In the above function called fetchEmpDetails we are just printing the value employee name of the class instance variable

2.We can modify the above class to print empNo attribute.We will access the empNo instance attribute using getter and setter as:

class Employee:
def __init__(self, empNo = 0):
self.set_empNo(empNo)

def get_empNo(self):
return self._empNo

def set_empNo(self, value):
if value < 0:
raise ValueError("empNo below 0 is invalid")
self._empNo = value

Now if you call the get_empNo() getter then value “15” will be printed.

emp = Employee(15)
print(emp.get_empNo())

 

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While loop in Python is used to execute statements repeatedly until a condition is satisfied. The condition is followed by
boolean expression.Following is the syntax of a while loop:

while boolean_expression:
    statements

Observe the following in the above code

• After the while keyword there is a colon (:) .The colon is used to introduce a block in Python.
• We have specified the statements in the while loop after whitespaces. This is a convention in Python to follow the block statements after indentation of 4 whitespaces.

Note that we have not used brackets in while loop.

In the following example we are setting the value of variable a as 1.Then we are incrementing the value of a and printing it till it is less than 10.So this loop will execute 10 times

a=1
while a<10:
a+=1
print(a)

break keyword

break is used exit the while block.So if you use the break keyword then the execution exits the while block.In the following example we are using the break keyword for exiting the while loop if the the value of variable a becomes equal to 5.

while a<10:
a+=1
if(a==5):
break
print(a)

 

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List is an ordered collection of values.Unlike other languages list elements in Python can be of different types.

Create a list in Python

1. To create a list declare list variable just like a normal variable.
2. Assign list of comma separated values inside square brackets

num_list=[1,2,3,4,5]

above will create list of numbers

to create list of strings use:

str_list=['a','b','c','random string']

Accessing list elements

As the elements in list are ordered so you can access them by index .to access the element of the list use index inside square brackets:

str_list[0] will return ‘a’

str_list[3] will return ‘random string’

Using negative index

to acess the elements relative to the last element use negative values So second last element can be accessed as:

str_list[-2]

and last element will be

str_list[-1]

adding new items to a list

Slicing

we can retrieve a part of the last from the original list.This is called slicing.To use slicing you specify start index followed by colon(:) and end index.For example to retrieve the first two elements from the above list in a new list use:

str_list[0:2]

this will return ‘a’,’b’ in a new list

Add elements to list

There are different ways of adding elements to list:

• using the plus (+) operator

 

      str_list=str_list+['d','e']

• using the append() method

 

 str_list.append('f')

•     using the insert() method

 

     str_list.insert(1,'0')

the item is inserted at the specified index.

Finding number of Items in a List

len(object) method is useful for finding the length of list.You can use this inbuilt method with other sequences such as tuples and dictionary as well.For example,you can use it as:

numbers=['1','2','3']
len(numbers)

 

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