Python

Lecture – 2 Lecture – 2

- Ravi Kiran Khareedi

Operators

• Operators are the functionality to perform

some work.

• They need some thing to work on – They are

called Operands.called Operands.

• Ex: sum = a + b;

• + , = ->Operators

• Sum, a,b -> Operands

Operators

• + -> Add

• - -> Subtract

• * -> Multiply

• / -> Divide

• ** -> Power of• ** -> Power of

• = -> Assignment

• % -> Modulus

• << -> Left Shift

• >> -> Right Shift

Operators (Cont)

Comparison Operators:

> Greater than

< Less than

== Equal to

<= Less Than or equal to<= Less Than or equal to

>= Greater than or equal to

!= Not equal to

Operators (Cont)

Bitwise Operators

• & - Bitwise And

• | - Bitwise Or

• ^ - Bitwise Xor• ^ - Bitwise Xor

• ~ - 1’s complement

Operators(Cont)

Logical Operators

• And

• Or

• Not• Not

Precedence

• Consider 2+3*4

• Guess the answer ?

• Are we sure which operation to perform first • Are we sure which operation to perform first

in an expression?

• To do this we need to know which operator

has higher priority than the other. This is

nothing but PRECEDENCE.

Precedence

Note : We haven’t seen few operators. For now it can ignored.

Chapter : CONTROL FLOW

Control Flow

• Use to alter the flow of execution

• Without Control Statements, the flow of

execution is always sequential.

• 3 Control Statements: • 3 Control Statements:

– if

– for

– while

if statement

• ‘if’ statement is used to check the condition. (Execute certain statements based on certain conditions)

• If (condition is true)

{ # Some statements here}{ # Some statements here}

Else

{ # Some statements here}

NOTE: Code grouping in Python is done based on indentation. {} are not allowed

Example

a = 5;

if (a == 5):

print "ok !"

else:

print "Not ok";

Print “End”;

TASK :

1. Try with out else

2. Try with Elif

Nested If’s

if expression1:

statement(s)

If expression2:

statement(s)

elif expression3:

statement(s) statement(s)

else

statement(s)

elif expression4:

statement(s)

else:

statement(s)

While statement

while expression:

statement(s)

• Ex:

i = 1i = 1

while (i < 10):

print i;

i = i + 1;

print “Done”;

For statement

for iterating_var in sequence:

statements(s)

Ex:Ex:

for i in range(1, 5):

print i

Break statement

• Used to stop the execution of a looping

statement,

– even if the loop condition hasn’t become false.

– Or the sequence of items has been completely – Or the sequence of items has been completely

iterated over.

Using break

for i in range(1 , 20):

if(i == 10):

break;

print i;

Continue statement

• The continue statement is used to tell Python

to skip the rest of the statements in the

current loop block and to continue to the next

iteration of the loop.iteration of the loop.

Continue Usage

for i in range(1 , 20):

if(i == 10):

continue;

print i;print i;

Else block’s in looping Statements

• Python supports to have an else statement

associated with a loop statements.

• If the else statement is used with a for loop, the else

statement is executed when the loop has exhausted statement is executed when the loop has exhausted

iterating the list.

• If the else statement is used with a while loop, the

else statement is executed when the condition

becomes false.

TASK

• Print the even numbers from 1 to 20 using for

loop and while loop.

• Print the numbers from 1 to 20 skipping the

multiples of 5. (Don’t print 5, 10, 15 )multiples of 5. (Don’t print 5, 10, 15 )

For statement, bit more

for i in range(1 , 20, 2):

print i;

3rd argument specifies the step size for 3rd argument specifies the step size for

incrementing i

Chapter: Functions

Functions

• Functions are a reusable piece of program.

• In simple words, it’s a block of statements

which has a name.

• We can run a function from anywhere in the • We can run a function from anywhere in the

program, any number of times using its name,

this is called “Function Calling”.

Functions: Usage

• Functions are defined using def

• Syntax:

def fnName():

Statement(s)Statement(s)

EX:

def sayHello():

print 'Hello World!' # block belonging to the function

# End of function

sayHello() # call the function

Function Parameters

• A function can take parameters which are just values you supply to the function so that the function can do something utilising those values

• Ex:def printMax(a, b): # These are Function Parametersdef printMax(a, b): # These are Function Parameters

if a > b:

print a, 'is maximum'

Else:

print b, 'is maximum'

printMax(3, 4) # directly give literal values

X = 5

y = 7

printMax(x, y) # give variables as arguments

TASK

• Guess the output:a = 10;

def fun():

a = 5;

print a , "- inside function";print a , "- inside function";

fun();

print a, " - Outside function";

Local Variables

• Variable defined inside a function is limited to

the scope of the function.

• They are different from the variables of same

name outside the function. name outside the function.

Global Variables

def func():

global x

print 'x is', x

x = 2

print 'Changed global x to', xprint 'Changed global x to', x

x = 50

func()

print 'Value of x is', x

- We should try to avoid using global.

Default Argument Values

• For some functions, you may want to make

some of its parameters as optional and use

default values if the user does not want to

provide values for such parameters – This is provide values for such parameters – This is

Default ArgumentsEx:

def say(message, times = 1):

print message, times

say ('Hello');

say ('World', 5);

TASK

Valid or Invalid Statements ?

• def fun(a , b =5)

• def fun (a=5, b)

• def fun(a=5, b =3)

Note: Default Arguments

• Only those parameters which are at the end of the parameter

list can be given default argument values i.e. you cannot have

a parameter with a default argument value before a

parameter without a default argument value in the order of

parameters declared in the function parameter list.parameters declared in the function parameter list.

• This is because the values are assigned to the parameters by

position

Keyword Arguments

• In case of large number of parameters, Default

arguments may be difficult to use.

• So Python Supports Keyword arguments.

• It provides more flexibility• It provides more flexibility

• Note: You cannot have a parameter with a default argument

value before a parameter without a default argument value

Advantages of Keyword Arguments

There are two advantages –

• Using the function is easier since we do not

need to worry about the order of the

arguments. arguments.

• We can give values to only those parameters

which we want, provided that the other

parameters have default argument values.

return statement

• The return statement is used to return from a function i.e. break out of the function.

• We can optionally return a value from the function as well.

• Ex:• Ex:def maximum(x, y):

if x > y:

return x

else:

return y

print maximum(2, 3)

References

• Python Tutorial by Tutorialspoint.com

• A Byte of Python by Swaroop C H