Loops in Python

Introduction Loops in Python

A concept in Python programming package that allows repetition of certain steps, or printing or execution of the similar set of steps repetitively, based on the keyword that facilitates such functionality being used, and that steps specified under the keyword automatically indent accordingly is known as loops in python. Its acting as a block, with “while” continuing to execute until a certain specified condition is met, and “for” executing till the index variable in the specified range of values reaches its final value.

Looping is a common phenomenon in any programming language, From a python perspective, the powerful programming language offers two broad categories of loops. They are as below:

• While Loops
• For loops

While Loops

The common strategy behind while loops are they execute a set of statements until the given condition is satisfied. The next statement call happens at the instance when the specified condition is satisfied. The segment or the body of the loop is determined by the use of indented code segments. Indentation starts the loop and the line from which it starts to be unindented represents the end of the mentioned loop. All non zero values are interpreted as true here.

Flowchart

Example

Code

while condition:
# execute these statements
else:
# execute these statements

Code Snippet

n = 10
sum = 0
i = 1
while i <= n:
sum = sum + i
i = i+1
print("The sum is", sum)

While Loop Example

Python Program for Matching a String

Import Section 

• import string
• import random
• import time

Variable section

endeavourNext = ''
completed = False
iterator = 0

Propable Characters to Compare

propableCharacters = string.ascii_lowercase + string.digits + string.ascii_uppercase + ' ., !?;:'

String to Be Generated

t = input("Enter the expected string or word : ")

Generate the Initial Random String

endeavourThis = ''.join(random.choice(propableCharacters)
for i in range(len(t)))

Iterate While Completed Is False

while completed == False:
print(endeavourThis)
endeavourNext = ''
completed = True
for i in range(len(t)):
if endeavourThis[i] != t[i]:
completed = False
endeavourNext += random.choice(propableCharacters)
else:
endeavourNext += t[i]

Increment the iterator

iterator += 1
endeavourThis = endeavourNext
time.sleep(0.1)

Driver Code 

print("Target match found after " +
str(iterator) + " iterators")

For Loops

For traversing a sequential statement set these loops are implied. The persistence of the loop is passed on pending the last item in the series is executed. While loop here to the content of the loop is separated from the rest of the code by introducing the indentation. As like while loop here to indentation plays an important role in determining the body of the loop involved. Indentation starts the loop and the line from which it starts to be unindented represents the end of the mentioned loop.

Flowchart

Example

for iterator_var in sequence:
statements(s)

Code Snippet

# Iterating on String
print("\nString Iteration")
string1 = "hello"
for i in string1 :
print(i)

For Loop Example#1

Python Program Using Turtle Graphing Technique

Import turtle

Function Definition

def border(obj1, panel_x, panel_y):
obj1.penup()
obj1.home()
obj1.forward(panel_x / 2)
obj1.right(90)
obj1.forward(panel_y / 2)
obj1.setheading(180)
obj1.pencolor('red')
obj1.pendown()
obj1.pensize(10)
for distance in (panel_x, panel_y, panel_x, panel_y):
obj1.forward(distance)
obj1.right(90)
obj1.penup()
obj1.home()
def square(obj1, size, color):
obj1.pencolor(color)
obj1.pendown()
for i in range(4):
obj1.forward(size)
obj1.right(90)
def main():
panel = turtle.Screen()
panel.title('Square Demo')
panel_x, panel_y = panel.screensize()
obj1 = turtle.Turtle()
border(obj1, panel_x, panel_y)
colors = ['red', 'orange', 'yellow', 'green', 'blue', 'violet'] obj1.pensize(3)
for i, color in enumerate(colors):
square(obj1, (panel_y / 2) / 10 * (i+1), color)
print('Hit any key to exit')
dummy = input()

Main Program Call

if __name__ == '__main__':
main()

For Loop Example#2

Program to concatenate two LISTS into a dictionary.

Variable declaration

Key_elements=[] value_elements=[]

Count to be processed

var1=int(input("Count of elements for the dictionry:"))

print (Key Elements)

for x in range(0,var1):
element=int(input("Element item entered" + str(x+1) + ":"))
Key_elements.append(element)

Print (Value Elements)

for x in range(0,var1):
element=int(input("Element item entered" + str(x+1) + ":"))
value_elements.append(element)
d=dict(zip(Key_elements,value_elements))
#Print Section
print("The formulated dictionary is:")
print(d)

Nested loops

Nested looping is the process of looping one loop within the boundaries of others. So when the control flows from the outer loop to the inner loop it returns back to the outer-loop only when the inner loops are completed. Indentation is used to determine the body of the nested loops. Indentation starts the loop and the line from which it starts to be unindented represents the end of the mentioned loop.

Example

Code:

for iterating_variable#1 in sequence#1:
for iterating_variable#2 in sequence#2:
statements(s)
statements(s)
while expression#1:
while expression#2:
statement(s)
statement(s)

Nested Loop Example

Python  Program for File Handling

import os
def listfile(types):
current_path,filename = os.path.split(os.path.abspath(__file__))

Nested Looping Section in The Program

Outer  For Loop
for path,dir,file in os.walk(current_path):
file_name = str(file)

Inner For Loop

for type in types:
if file_name.endswith(type):
print(file_name)
def deletefile(types):
choice2 = input("Please enter the file to delete : ")
os.remove(choice2)
types = [".txt']",".srt]",".py]"]

Header Area

print(" = = = = = = = = = = = = = = = = = = = = = " )
print(" $$$$$$$$$$$$$ FILE HANDELING $$$$$$$$$$$$ ")
print(" = = = = = = = = = = = = = = = = = = = = = ")

File Listing

File_list = listfile(types)

File Operation

print("                      ")
print(" %%%%%%%%%%%%%%%%%%%%")
print(" SELECT AN OPERATION ")
print(" %%%%%%%%%%%%%%%%%%%%")
print( " DEL - Delete a file Type ")
print( " END - EXIT ")
choice = input(" Please enter the desired operation : ")
if choice == 'DEL':
File_deletion = deletefile(types)
listfile(types)
exit
if choice == 'END':

Print( Bye Bye )

exit
else:

Print( Invalid Option )

exit

Python Loop Control Statements

Loops iterate above a block of code pending expression in testis false, but when there is an instance where we need to stop the loop without a check to the condition that is were the loop control statements come into play. The three major loop control statements in python are as below:

• Break: Terminates the loop and passes the control to the statement after the loop. If a break is mentioned into a nested loop then it is the innermost loop is where the break will initially terminate.
• Continue: Skips the remaining sentences in the loop and checks the condition posted in the loop.
• Pass: It just passes the execution when reaching a specific statement.

Loop Control Statements example

Python Program Using Loop Control Statements

var_a = 1
var_b = 2
while var_a < var_b:
print(" Code enters while loop ")
var_c = ["SUV","sedan","hatchback","End"] for iterator in var_c:
if iterator == "SUV":
print("Hyundai creata")
print("Mahindra bolero")
print("---------------")
if iterator == "sedan":

Loop Control Statement: Pass

pass
if iterator =="hatchback":
print("Renault Kwid")
print("suzuki alto")
print("---------------")
if iterator == "End":

Loop Control Statement: Break

break
var_a = var_a+1

Benefits of python Loops: The key advantages of loops are as below:

• Code reduction.
• Reduces code complexity.
• Brings in more stability into coding.
• Code redundancy is greatly resolved.

Conclusion – Loops in Python

The dominance exhibited by any programming language depends on the classified set of coding functionalities. In such instance, python programming’s looping structure is largely stable and flexible to code which stands out to be among the prior reasons which make this language to dominate the market.

Recommended Articles

This has been a guide to Loops in Python. Here we discuss what are the Loops in Python, While loops and much more with appropriate sample code. You can also go through our other suggested articles to learn more –

1. Python vs C++
2. Python Collections
3. Python File Operations
4. Dictionary in Python