Python: Looping Statemnts

Looping Statements in Python:

Looping statements are used to execute the set of statements Repeatedly.

Python supports 2 types of Loops, they are

• while loop
• for loop

While Loop:

While loops executes the set of statements are repeatedly until condition will become False.

                                          (or)

While loops executes the repeatedly until while condition is False.

syntax 1:

                           while  condition :  statement

syntax 2:

                           while condition:

                                           statement 1

                                           statement 2

                                           --------------

                                          --------------

                                         statement n

Example 1:

i=1

sum=0

while i<=100:

    sum=sum+i

    i=i+1

print(sum)

Output:

5050

Example 2:

a=0

while a<5:

    print(a)

    a+=1

Output:

0

1

2

3

4

While loop with else:

syntax:

                         while  condition:

                                            statement 1

                                            statement 2

                                            ---------------

                                            ---------------

                                            statement n

                        else:

                              statement 1

                              statement 2

                              ---------------

                              ---------------

                              statement n

Infinite while loop:

• Executing no.of times keep on upto sufficient memory.
• in order to work with the infinite loops,we are using break statement

syntax:

                             while  True:

                                          -------------

                                          -------------

                                          -------------

                                          -------------

Example 1:

i=1

while True:

    print("hai siva")

    if i==5:

            i=i+1

Output:

hai siva

hai siva

hai siva

hai siva

hai siva

hai siva

hai siva

hai siva

hai siva

hai siva

hai siva

hai siva

............

...........

............

............

Traceback (most recent call last):

  File "E:/python_practice/examples/infinite while.py", line 3, in <module>

    print("hai siva")

  File "C:\Program Files\Python35\lib\idlelib\PyShell.py", line 1344, in write

    return self.shell.write(s, self.tags)

Keyboard Interrupt

Note:

solve the problems in infinite loops, we are going to use break statement

Example 2:

i=1

while True:

    print("hai siva")

    if i==5:

        break

    i=i+1

Output:

hai siva

hai siva

hai siva

hai siva

hai siva

break statement:

• break statement is used in the looping statements.
• when ever break statement of the loop is executed an automatically control will come out from the loop.
• Generally we use the break statement to exit from the infinite loops.

Example:

i=1

while True:

    print("hai siva")

    if i==5:

        break

    i=i+1

else:

    print("hai krishna")

Output:

hai siva

hai siva

hai siva

hai siva

hai siva

• we can use the else block with the while loop in python,when ever while loop condition becomes False,then only control will goto the else block.
• if we are exiting from the while loop,by executing break statement when control will not go to the else block.

continue statement:

• continue statements are used in loops.
• skipping the particular iteration
• when ever continue statement of the loop is executed can without executing the remaining part of that particular iteration when control will goto the next iteration.

Example:

i=0

while i<5:

    i=i+1

    if i==2:

        continue

    print("hai siva",i)

else:

    print("hai krishna")

Output:

hai siva 1

hai siva 3

hai siva 4

hai siva 5

hai krishna

using continue and break statements in a single program

 Example: Login form

while True:

    name=input("enter UserName: ")

    if name!= 'siva':

        continue

    password=input("Helo siva, enter your PassWord ?  ")

    if password=='krishna@143':

        break

print("Access Granted")

Output:

enter UserName: siva

Helo siva, enter your PassWord ?  krishna@143

Access Granted

Output 2:

enter UserName: abc

enter UserName: xyz

enter UserName: siva

Helo siva, enter your PassWord ?  krishna

enter UserName: siva

Helo siva, enter your PassWord ?  krishna@142

enter UserName: siva

Helo siva, enter your PassWord ?  krishna@143

Access Granted

Note:

• Here continue and break statements are written in the if conditions,but both are working based on loops.

for  loop:

• for loop executes the set of statements with respect to every element of the collection object.

Syntax:

                               for  variablename  in collvariable :

                                                               ----------------------

                                                               ----------------------

                                                               ----------------------

Example 1:

x=[10,20,30,40,50]

for p in x:

    print(p)

Output:

10

20

30

40

50

Example 2:

x="sivakrishna"

for p in x:

    print(p)

Output:

s

i

v

a

k

r

i

s

h

n

a

Note:

• for loop takes string object also,but string object is not a collection object.
• string object is a group of  characters.

Some times We are not interested blocks, simply that blocks are passed by using pass keyword. 

Example:

                if  condition :

                          pass