Iteration in Python

1. ITERATIONS
PROF POOJAB S

2.  while statements
 Infinite loop and break
 Finishing iterations with continue
 Definite loops using for
 Loop Pattern
 Counting and Summing loops
 Maximum and Minimum loops
Iteration

3. The while Statement
 Syntax:
while condition:
Statement 1
Statement 2
…..
Statement N
Statements after while
 while: keyword
conditions will be evaluated and leads True or False
if True Statements will be executed else exits.

4.  Eg:
1. n=1
while n<=5:
print(n)
n=n+1
print("Over")
2. n=5
while n>=0:
print(n)
n=n-1
print("Exit")

5.  Loop execute infinite number of times.
 Eg:
n=1
while True:
print(n)
n=n+1
 Above program, loop condition is True, so it will never exits.
 If we want to come out from the loop, we use break.
 Eg:
n=1
while True:
print(n)
n=n+1
break
Infinite Loops, break and continue

6.  Eg:
1. while True:
x=int(input("Enter a Number:"))
if x>=0:
print("You have entered a positive number. The number is:",x)
else:
print("You have entered a negative number")
2. while True:
x=int(input("Enter a Number:"))
if x>=0:
print("You have entered a positive number. The number is:",x)
else:
print("You have entered a negative number")
break

7. while True:
line=input(">")
if line=='done':
break
print(line)
print('Done!')

8.  Move to next iterations , use continue statement.
 Eg:
sum=0
count=0
while True:
x= int (input ("Enter a Number:"))
if x%2==0:
continue
else:
sum=sum+x
count=count+1
if count==5:
break
print("Sum=",sum)
continue statement

9. Definite Loops using for

10.  Syntax of for loop:
for var in list/sequence:
Statement 1
Statement 2
…..
Statement N
Statements after for loop
 for and in are keywords
list/ sequence is a set of elements on which the loop iterates
statements constitutes the body of loop

11.  Eg:
names=['Ram','Shyam','Raj']
for x in names:
print("Happy New Year",x)
print('Done!')
 List is an important data type.
 Can take elements of different types.
 Elements enclosed within square brackets.
 Elements can be extracted using index.
 If there are fixed set of numbers to iterate in a for loop, we can use range()

12.  range(start, end, steps)
Start: starting values
End: ending values but excluding ending value
Steps: increment/ decrement [default value is 1]
1. for i in range(5):
print(i,end='t')
2. for i in range(5,0,-1):
print(i,end='t')
3. for i in range(0,10,2):
print(i,end='t')

13.  while and for loop used to go through a list of items and check max or min data values.
1. Initialize one/more variables before loop starts.
2. Perform computation
3. Look result
 Counting and Summing Loops:
count=0
for i in [4,-2,41,34,25]:
count=count+1 #COUNT
print("Count=",count)
total=0
for i in [4,-2,41,34,25]:
total=total+I #SUMMATION
print("Total=",total)
Loop Patterns

14. big=None
print("Before Loop:",big)
for x in [12,0,21,-3]:
if big is None or x>big: #MAXIMUM
big=x
print("Itearation Variable:",x,'Big',big)
print("Biggest:",big)
small=None
print("Before Loop:",small)
for x in [12,0,21,-3]:
if small is None or x<small: #MINIMUM
small=x
print("Iteration Variable:",x,'Small',small)
print("Smallest:",small)