Python while and for Loop Statments

Loops are indeed very powerful as it allows us to do a repetitive task that is to execute statement or group of statements multiple times. Python provides following types of loops to handle repetitive tasks: for and while loops.

The semantics of the while loop:

while condition:
    body containing (statment/s)

The semantics of the for loop:

for item in list:
     statement/s

Example 1 (for):

#Program to print each character in a string (which is a sequence of characters)

string = "Python"

#for each charachter in a string do this: print(char,end = '')

for char in string:
    print(char,end = '') #Output:Python

Example 2 (for):

#Program to print the first 5 positive even numbers
#Note:loops runs from 0-9 increment by 1

for number in range(0,10):
    #even if evenly divisible by 2
    if( number%2 == 0):
        print(number,' is even')

#Alternative way, the range function also takes "step" as a parameter
#from 0-9 increment by 2

for number in range(0,10,2):
        print(number,' is even')

Output:

0  is even
2  is even
4  is even
6  is even
8  is even
0  is even
2  is even
4  is even
6  is even
8  is even

Example 3 (nested-for ):

#nested for loop

#Program to print number pattern such as this
#1
#12
#123
#1234
#12345
#123456
#1234567

for outer in range(1,8):
    for inner in range(1,outer+1):
        print(inner,end ='')
    print()

Output:

1
12
123
1234
12345
123456
1234567 

Example 1 (while):

#program to add the first 100 positive numbers

limit = 100
count = 1
sum =0

while count<=limit:
    sum+=count
    count+=1 #increment count by 1, there is no ++ operator in python :(

print(sum) #Output:5050

Example 2 (while):

#Countdown program

count  = 10
limit = 0

while count>=limit:
    print(count, end='-> ')
    count-=1; #decrement count by 1
    
print('Go!')

Output:

10-> 9-> 8-> 7-> 6-> 5-> 4-> 3-> 2-> 1-> 0-> Go!

Example 3 (nested while ):

#Program to print number pattern such as this
#1
#12
#123
#1234
#12345
#123456
#1234567

end = 7
start = 1

while start<=end:
    inner_start = 1
    inner_end = start
    while inner_start<=inner_end:
         print(inner_start,end ='')
         inner_start+=1
    start+=1
    print()

Output:

1
12
123
1234
12345
123456
1234567 

NOTE: there is no do-while loop in Python. However, it is possible to emulate the do-while loop as shown below.Use the while-True form shown below with an inner if-break when a do-while loop would have been appropriate.
Enhanced while-loop semantics:

while True:
    <setup code>
    if not <condition>:
        break
    <loop body>