Loops in Python

Last Updated : 8 May, 2026

Loops are used to execute a block of code repeatedly until a condition is met or all items in a sequence are processed. The main types are For loops (iterating over sequences) and While loops (executing code based on a condition).

For Loop

For loops is used to iterate over a sequence such as a list, tuple, string or range. It executes a block of code once for each item in the sequence.

Python 
n = 4
for i in range(0, n):
    print(i)

Output
0
1
2
3

Explanation:

  • n = 4 stores the ending value for the loop.
  • range(0, n) generates numbers from 0 to 3.
  • for i in range(0, n): iterates through each number in the range.

Below is the flowchart of For loop:

forloop
Flowchat of For Loop

Iterating by Index of Sequences

A for loop can also iterate through sequence elements using their index values with the help of range() and len().

Python 
a = ["geeks", "for", "geeks"]
for idx in range(len(a)):
    print(a[idx])

Output
geeks
for
geeks

Explanation:

  • len(li) returns the total number of elements in the list.
  • range(len(li)) generates index values from 0 to 2.
  • li[index] accesses list elements using their index.

While Loop

While loop repeatedly executes a block of code as long as the given condition remains true. When the condition becomes false, the line immediately after the loop in the program is executed.

Python 
cnt = 0
while (cnt < 3):
    cnt = cnt + 1
    print("Hello Geek")

Output
Hello Geek
Hello Geek
Hello Geek

Explanation:

  • cnt = 0 initializes the counter variable.
  • while (cnt < 3): runs the loop while the condition is true.
  • cnt = cnt + 1 increases the counter value by 1.

Below is the flowchart of While loop:

ff
Flowchart of While loop

Infinite While Loop

An infinite while loop runs continuously because its condition always remains true.

Python 
while (True):
    print("Hello Geek")

Explanation:

  • while(True): creates a loop with a condition that is always true.
  • print("Hello Geek") keeps executing repeatedly inside the loop.

Note: It is suggested not to use this type of loop as it is a never-ending infinite loop where the condition is always true and we have to forcefully terminate the program (or loop execution).

Nested Loops

A nested loop is a loop inside another loop. The inner loop executes completely for every iteration of the outer loop.

Python 
for i in range(1, 5):
    for j in range(i):
        print(i, end=' ')
    print()

Output
1 
2 2 
3 3 3 
4 4 4 4

Explanation:

  • Outer loop for i in range(1, 5) controls the number of rows and Inner loop for j in range(i) runs i times for each row.
  • print(i, end=' ') prints the value of i on the same line and print() moves output to the next line after each row.

Recommended Problems: For loop, For Loop 1, For Loop 2, While Loop, Jumping through While

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