FOR loop

Good Morning students

Today we will look at the comparison between WHILE and FOR loops and see how the FOR loop works.
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The Google meet link for today's class is :

meet.google.com/awj-jydm-ask

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By the end of today's session, you will be able to:

• Differentiate between CONDITIONAL and COUNTING Loops.
• Understand the working of the FOR loop
• Apply the knowledge to create appropriate FOR loops to give the desired results.

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CONDITIONAL LOOP:

• The loops that repeat until a certain thing happens
• They keep repeating as long as some condition is true.
• Therefore, we can say that WHILE loop is conditional loop
• We cant say in advance, how many times this loop will execute.

 COUNTING LOOPS:

• The loops that repeat a certain number of times
• it is designed to process the items of any sequence, such as a list or string , one by one
• FOR loop is a counting loop

The general form of FOR LOOP is as given below:

for variable in sequence :
     statements_to_repeat

Syntax

for iterating_var in sequence:
   statements(s)

If a sequence contains an expression list, it is evaluated first.

 Then, the first item in the sequence is assigned to the iterating variable iterating_var.

Next, the statements block is executed. 

Each item in the list is assigned to iterating_var, and the statement(s) block is executed until the entire sequence is exhausted.

Flow Diagram

For example, consider the following loop:

for a in [1,4,7]:
      print(a)
      print(a*a)

In the above example, variable a will be assigned each value of list one by one,

•   for the first time a will be 1
•   then  a will become 4
•   and finally a will become 7 

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• The body of the loop is showing in the pink colour. 
• All statements in the body of the loop will be executed for each value of loop variable a 
• i.e. for a=1 , then for a=4 then for a=7  

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A loop in Python is processed as

• The loop-variable is assigned the first value in the sequence
• All the statements in the body of the FOR loop are executed with assigned value of loop variable (STEP 2)
• Once STEP 2 is over, the loop variable is assigned the next value in the sequence and the loop-body is executed(i.e. STEP 2 repeated) with the new value of loop-variable
• This continues until all values in the sequences are processed.
• It has the ability to iterate over the items of any sequence, such as a list or a string.

Example

Live Demo

#!/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!"

When the above code is executed, it produces the following result −

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!