Python programming –part 3

Python Programming –Part III
Megha V
Research Scholar
Kannur University
02-11-2021 meghav@kannuruniv.ac.in 1

Control flow statements
• Decision control flow statements (if, if…..else, if…….elif….else, nested
if)
• Loop(while, for)
• continue statement
• break statement

Decision making
• Decision making is required when we want to execute a code only if a certain condition is
satisfied.
1. if statement
Syntax:
if test expression:
statement(s)
Example:
a = 15
if a > 10:
print("a is greater")
Output:
a is greater

Decision making
2. if……else statements
• Syntax
if expression:
body of if
else:
body of else
• Example
a = 15
b = 20
if a > b:
else:
print("b is greater")
Output:
b is greater

Decision making
3. if…elif…else statements
elif - is a keyword used in Python replacement of else if to place another
condition in the program. This is called chained conditional.
If the condition for if is False, it checks the condition of the next elif block and so on. If
all the conditions are false, body of else is executed.
• Syntax
if test expression:
body of if
elif test expression:
body of elif
else:
body of else

Decision making
• if…elif…else statements
Example
a = 15
b = 15
if a > b:
elif a == b:
print("both are equal")
else:
print("b is greater")
Output:
both are equal

Decision making
4. Nested if statements
if statements inside if statements, this is called nested if statements.
Example:
x = 41
if x > 10:
print("Above ten,")
if x > 20:
print("and also above 20!")
else:
print("but not above 20.")
Output:
Above ten,
and also above 20!

LOOPS
• There will be situations when we need to execute a block of code several
times.
• Python provides various control structures that allow repeated execution
for loop
while loop
for loop
• A for loop is used for iterating over a sequence (that is either a list, a tuple, a
dictionary, a set, or a string).
• With the for loop we can execute a set of statements, once for each item in a
list, tuple, set etc.

LOOPS
for loop
Syntax:
for item in sequence:
Body of for
• Item is the variable that takes the value of the item inside the sequence of each
iteration.
• The sequence can be list, tuple, string, set etc.
• The body of for loop is separated from the rest of the code using indentation.

LOOPS
for loop
Example Program 1:
#Program to find the sum of all numbers stored in a list
numbers = [2,4,6,8,10]
# variable to store the sum
sum=0
# iterate over the list
for item in numbers:
sum = sum + item
#print the sum
print(“The sum is",sum)
Output
The sum is 30

LOOPS
for loop
Example Program 2:
flowers = [‘rose’,’lotus’,’jasmine’]
for flower in flowers:
print(‘Current flower :’,flower)
Output
Current flower : rose
Current flower : lotus
Current flower : jasmine

LOOPS
• for loop with range() function
• We can use range() function in for loops to iterate through a sequence of numbers,
• It can be combined with len() function to iterate through a sequence using indexing
• len() function is used to find the length of a string or number of elements in a list,
tuple, set etc.
• Example program
flowers=[‘rose’,’lotus’,’jasmine’]
for i in range(len(flowers)):
print(‘Current flower:’, flowers[i])
Output
Current flower : rose
Current flower : lotus
Current flower : jasmine

range() function
for x in range(6):
print(x)
• Note that range(6) is not the values of 0 to 6, but the values 0 to 5.
• The range() function defaults to 0 as a starting value, however it is possible to
specify the starting value by adding a parameter: range(2, 6), which means values
from 2 to 6 (but not including 6)
• The range() function defaults to increment the sequence by 1, however it is
possible to specify the increment value by adding a third parameter: range(2,
30, 3):
• increment the sequence with 3 (default is 1):
for x in range(2, 30, 3):
print(x)

LOOPS
enumerate(iterable,start=0)function
• The enumerate() function takes a collection (eg tuple) and returns it as an enumerate object
• built in function returns an e
• numerate object
• The parameter iterable must be a sequence, an iterator, or some other objects like list which supports iteration
Example Program
# Demo of enumerate function using list
flowers = [‘rose’,’lotus’,’jasmine’,’sunflower’]
print(list(enumerate(flowers)))
for index,item in enumerate(flowers)
print(index,item)
Output
[(0,’rose’),(1,’lotus’),(2,’jasmine’),(3,’sunflower’)]
0 rose
1 lotus
2 jasmine
3 sunflower

LOOPS
2. while loop
Used to iterate over a block of code as long as the test expression (condition) is True.
Syntax
while test_expression:
Body of while
Example Program
# Program to find the sum of first N natural numbers
n=int(input(“Enter the limit:”))
sum=0
i=1
while(i<=n)
sum = sum+i
i=i+1
print(“Sum of first ”,n,”natural number is”, sum)
Output
Enter the limit: 5
Sum of first 5 natural number is 15

LOOPS
while loop with else statement
Example Program
count=1
while(count<=3)
print(“python programming”)
count=count+1
else:
print(“Exit”)
print(“End of program”)
Output
python programming
python programming
python programming
Exit
End of program

Nested Loops
• Sometimes we need to place loop inside another loop
• This is called nested loops
Syntax for nested for loop
for iterating_variable in sequence:
for iterating_variable in sequence:
statement(s)
statement(s)
Syntax for nested while loop
while expression:
while expression:
statement(s)
statement(s)

CONTROL STATEMENTS
• Control statements change the execution from normal sequence
• Python supports the following 3 control statements
• break
• continue
• pass
break statement
• The break statement terminates the loop containing it
• Control of the program flows to the statement immediately after the body of the
loop
• If it is inside a nested loop, break will terminate the innermost loop
• It can be used with both for and while loops.

CONTROL STATEMENTS
break statement
• Example
#Demo of break
for i in range(2,10,2):
if(i==6):break
print(i)
print(“End of program”)
Output
2
4
End of program
Here the for loop is intended to print the even numbers from 2 to 10. The if condition checks
whether i=6. If it is 6, the control goes to the next statement after the for loop.

CONTROL STATEMENTS
continue statement
• The continue statement is used to skip the rest of the code inside a
loop for the current iteration only.
• Loop does not terminate but continues with next iteration
• continue returns the control to the beginning of the loop
• rejects all the remaining statements in the current iteration of the
loop
• It can be used with for loop and while loop

CONTROL STATEMENTS
continue statement
Example
for letter in ‘abcd’:
if(letter==‘c’):continue
print(letter)
Output
a
b
d

CONTROL STATEMENTS
pass statement
• In Python pass is a null statement
• while interpreter ignores a comment entirely, pass is not ignored
• nothing happens when it is executed
• used a a placeholder
• in the case we want to implement a function in future
• Normally function or loop cannot have an empty body.
• So when we use the pass statement to construct a body that does nothis
Example:
for val in sequence:
pass

Reading input
• The function input() consider all input as strings.
• To convert the input string to equivalent integers, we need to use
function explicitly
• Example
cost = int(input(Enter cost price:’))
profit = int(input(Enter profit:’))

LAB ASSIGNMENT
• Write a python program to find maximum of 3 numbers using if….elif…else
statement
• Program to find largest among two numbers using if…else
• Program to find the sum of first n positive integers using for loop
• Program to print prime numbers using for loop
• Python program to print prime numbers using while loop
• Program to print the elements in a list and tuple in reverse order

Python programming –part 3

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