What are the 3 types of loops in Python | for loop in python with condition

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This tutorial contains in-depth knowledge of Loops in python.

Lets begin!

Usually, statements are executed in a sequential way then loop is required. The first statement in function is executed first, then second and so on. There may be situations while coding in python, you will require to execute a block of code several times. To fulfill the need of that situation, you will require a loop function.

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The Python programming language provides various structures that allow it to execute complicated paths. A loop statement helps you to execute a single statement of a group of statements multiple times.

Three types of loops in python programming language are

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“For” loop

For loop allows a programmer to execute a sequence of statements several times, it abbreviates the code which helps to manage loop variables.

For loop syntax

for val in sequence:

Body of for

Here’s its flow chart, which will give you an idea about how it gets implemented.

If a sequence has a list of expressions, it is evaluated first. After this, the first item in the sequence is assigned to iterate with a value “iterating_var”. Next the block containing statements will be executed.

Now, each item in the list will be assigned to iterating_var and block having statements will be executed in the next step until the entire sequence is exhausted.

Live Code

#!/usr/bin/python

for letter in ‘Python’: # First Example

print ‘Current Letter :’, letter

fruits = [‘banana’, ‘apple’, ‘mango’]

for fruit in fruits: # Second Example

print ‘Current fruit :’, fruit

print “Good bye!”

The above code will result the output, which are shown below

Output

Current Letter : P

Current Letter : y

Current Letter : t

Current Letter : h

Current Letter : o

Current Letter : n

Current fruit : banana

Current fruit : apple

Current fruit : mango

Good bye!

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For loop using else statement

Python programming language allows a programmer to utilize the else statement associated with a loop statement. If the else statement is being utilized, then the else statement will be executed till the loop has exhausted iterating the list.

Below example illustrates the use of else statements with for loops that search for prime numbers from 10 to 20.

Live Demo

#!/usr/bin/python

for num in range(10,20): #to iterate between 10 to 20

for i in range(2,num): #to iterate on the factors of the number

if num%i == 0: #to determine the first factor

j=num/i #to calculate the second factor

print ‘%d equals %d * %d’ % (num,i,j)

break #to move to the next number, the #first FOR

else: # else part of the loop

print num, ‘is a prime number’

break

This output will be shown if the above code is executed properly.

10 equals 2 * 5

11 is a prime number

12 equals 2 * 6

13 is a prime number

14 equals 2 * 7

15 equals 3 * 5

16 equals 2 * 8

17 is a prime number

18 equals 2 * 9

19 is a prime number

“While” loop

While loop allows a programmer to repeat a single statement or a group of statements for TRUE condition. It verifies the condition before executing the loop.

While loop syntax in Python programming language

while expression:

statement(s)

Here, in the place of statements, it may be possible there is a single statement or a block of statements. The condition may contain any expression and it can be true for any non zero value. The loop will iterate every time when the value is found true. If the condition is found false, the program will follow the immediate next line of the loop.

In python programming language, all the statements are indebted by the same number of character space while writing a code for a single block. It always uses the method of indentation as a grouping statement.

Here is the important point of the while loop, which shows that the loop might not ever run. When the condition is found false, the loop body will be skipped and the statement of while loop will be implemented.

Example

Live Demo

#!/usr/bin/python

count = 0

while (count < 9):

print ‘The count is:’, count

count = count + 1

print “Good bye!”

Output

The count is: 0

The count is: 1

The count is: 2

The count is: 3

The count is: 4

The count is: 5

The count is: 6

The count is: 7

The count is: 8

Good bye!

Here the block which consists of the print and increment statements, is iterated until the count is no longer less than 9. With each execution, the current of the index count is increased by 1.

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The infinite Loop

A loop becomes an infinite loop if a condition never turns out to be FALSE. You should utilize alert when utilizing while loops as a result of the likelihood that this condition never makes plans to a FALSE. This outcomes in a loop that never ends. Such a loop is called an infinite loop.

An infinite loop may be valuable in client/server programming where the server needs to run persistently so client programs can speak with it as and when required.

Example

#!/usr/bin/python

var = 1

while var == 1 : # This constructs an infinite loop

num = raw_input(“Enter a number :”)

print “You entered: “, num

print “Good bye!”

Output

Enter a number :20

You entered: 20

Enter a number :29

You entered: 29

Enter a number :3

You entered: 3

Enter a number between :Traceback (most recent call last):

File “test.py”, line 5, in <module>

num = raw_input(“Enter a number :”)

KeyboardInterrupt

The iteration in the above example will not stop unless you do not exit the program by pressing CTRL+C command.

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“Nested” loops

Nested loop allows a programmer to use one or more loops inside any other for or while loop etc.

Syntax for “Nested” loops in python programming language

for iterating_var in sequence:

statements(s)

You can put any type of loop inside of any other type of loop using the nested loop. For example For loop can be inserted in while loop or vice versa.

Example

#!/usr/bin/python

i = 2

while(i < 100):

j = 2

while(j <= (i/j)):

if not(i%j): break

j = j + 1

if (j > i/j) : print i, ” is prime”

i = i + 1

print “Good bye!”

Output

2 is prime

3 is prime

5 is prime

7 is prime

11 is prime

13 is prime

17 is prime

19 is prime

23 is prime

29 is prime

31 is prime

37 is prime

41 is prime

43 is prime

47 is prime

53 is prime

59 is prime

61 is prime

67 is prime

71 is prime

73 is prime

79 is prime

83 is prime

89 is prime

97 is prime

Good bye!

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Conclusion: This is all about the three types of loops used in python programming language. If you want to explore more, you can join our online & offline courses at AIDM, which is one of the best python training institutes in Laxmi nagar Delhi.

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