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Loops in Python

1. while loop
2. for loop

1. While loop Python
2. For loop in Python
3. range() function in python
4. Else with loops

While loop Python

Syntax:

while (condition_1):
    this block will execute until condition_1 is true

Example:

# variable is assigned with value 0
i = 0

# This loop will run until 'i' is less than 5
# We need to update 'i' after every iteration, otherwise
# i will be always less than 5 and the loop will become an infinite loop
while (i<5):
    print("I am rapid coder")
    # increase i by 1
    i = i+1
    

Output:

I am rapid coder
I am rapid coder
I am rapid coder
I am rapid coder
I am rapid coder

For loop in Python

Syntax:

for var in sequence:
    block of code

Examples:

# This is a list, we will learn about it in detail in further articles
lst = ["Rapid","coders","akshay"]

for i in lst:
    # i will containe all values of lst one by one
    print(i)
    

Output:

Rapid
coders
akshay

# This is a dictionary, this is used to store key-value pairs
dic = {
    1 : "Rapid",
    2 : "coders",
    3 : "akshay",
}

for i in dic:
    print(i,end=" = ")
    print(dic[i])
    

Output:

1 = Rapid
2 = coders
3 = akshay

range() function in python

Syntax:

range(start,stop,step_size or jump size)

In the range function start and step_size is optional, if we will not specify then by default start will be zero and step_size will be 1. Let us understand the range function using code:

# range() function returns range object, it can be iterated using for loop
print(range(5))
print(type(range(5)))

# We will use type casting to convert it into a list for better understanding
# This will give a sequence from 0 to 9
# here start = 0 and step_size = 1 by default
# 10 will not be included in the sequence
a = range(10)
a = list(a)
print("a = ",end="")
print(a)

# here start = 5
b = range(5,10)
b = list(b)
print("b = ",end="")
print(b)

# here start = 5, stop = 20 and step_index = 2
c = range(5,20,2)
c = list(c)
print("c = ",end="")
print(c)

# here start = 5, stop = 50 and step_index = 5
d = range(5,50,5)
d = list(d)
print("d = ",end="")
print(d)
    

Output:

range(0, 5)
<class 'range'>
a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
b = [5, 6, 7, 8, 9]
c = [5, 7, 9, 11, 13, 15, 17, 19]
d = [5, 10, 15, 20, 25, 30, 35, 40, 45]

For loop using range

print("Loop 1")
for i in range(5):
    print(i)
    
print("Loop 2")
for i in range(5,10):
    print(i)
    
print("Loop 3")
for i in range(5,20,5):
    print(i)

Output:

    Loop 1
    0
    1
    2
    3
    4
    Loop 2
    5
    6
    7
    8
    9
    Loop 3
    5
    10
    15

Else with loops

Syntax(else with for):

for var in sequence:
    block of code
else:
    This code executes only when the loop exhausts

Syntax(else with while):

while (condition):
    block of code
else:
    This code executes only when the loop exhausts

Example:

for i in range(5):
    print(i)
else:
    print("Done with Loop")
    
for i in range(5):
    print(i)
        if(i==2):
            break
else:
    # This will not run because the loop is not exhausted
    # It is breaked using 'break' keyword
    # We will learn about 'break' in further article
    print("Not Done with Loop")

Output:

    0
    1
    2
    3
    4
    Done with Loop
    0
    1
    2