A Beginner’s Guide to Python Loops
Python loops—from basic for and while constructs to control flow tools (break, continue, else) and comprehensions—offer versatile and expressive ways to automate repetition in code. By combining good practices and Pythonic patterns, you’ll write clear, efficient, and maintainable loops that scale with complexity.
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WHAT IS A FOR LOOP IN PYTHON?
A for loop is used to repeat a block of code a certain number of times or for each item in a sequence (like a list, string, or range)
General syntax:
For a variable in sequence:
#code to run for each item
Variable: The name you give to the item in the sequence during each loop.
Sequence: A list, string, range, or anything iterable.
Indentation matters: everything inside the loop must be indented.
HOW TO WORK:
Think of it like a teacher taking attendance:
The teacher says each student’s name (loop variable) one by one (from the sequence).
For each name, they take some action (e.g., mark present)
Examples:
1. Loop through a list
fruits = ["apple", "banana", "cherry"]
2. Loop using range ()
for i in range(5): # 0 to 4
print(i)
3. loop with custom start and step
for i in range(2, 10, 2):
print(i)
output: 2 4 6 8
4.LOOP through a string
for letter in "python":
print(letter)
5. Loop with an if condition
6. Nested for loop
for i in range(1, 4):
for j in range(1, 4):
print(f"i={i}, j={j}")
7. Using for with enumerate ()
8. Loop through a dictionary
9. Loop with break
if num == 5:
break
print(num)
10. Loop with continue
for n in range(5):
if n == 2:
continue
print(n)
WHAT IS A WHILE LOOP IN PYTHON?
A while loop repeatedly executes a block of code as long as a given condition is true.
Syntax:
While condition:
#code block
Condition: A boolean expression(true or false).
The loop keeps running until the condition becomes false.
You must make sure something inside the loop changes to stop it eventually. Otherwise, you get an infinite loop.
Examples:
1. Basic counting loop
2. infinite loop (with break to stop)
3. countdown
num = 5
while num > 0:
Print (num)
num -= 1
4. Loop with user input
Password = ” “
while password != ”python”:
password= input(“enter password: ”)
print(“access granted”)
5. Sum of the first N numbers
n=5
total=0
total += i
i+=1
print (“sum:”, total)
6. Using continue in a while loop
i = 0
while i < 5:
i += 1
if i == 3:
continue
print(i)
7. Reverse a string
text = “python”
i = len (text)-1
while i >= 0:
print(text[i],end=””)
i-=1
8. Guess the number game
Secret = 7
guess=0
while guess != secret:
guess = int (input (“Guess the number:”))
print(“you guessed it!”)
9. Multiplication table
num = 3
i=1
While i <=10:
Print(f”{num} * {i} = {num*i}”)
i += 1
10. Factorial calculation
n = 5
fact =1
while n >0:
fact *=n
n-=1
print(“Factorial:”,fact)
CONDITIONAL STATEMENTS IN PYTHON:
Pass statement:
Purpose: Acts as a placeholder when a statement is syntactically required but you don’t want to do anything yet.
Effect: Does nothing ___the loop or block moves on.
Example:
1. for num in range(5):
if num ==2:
pass #do nothing for number 2
else:
print(num)
2. continue statement
Purpose: skip the current iteration and move to the next loop iteration.
Effect: The loop does not stop_ it just skips the rest of the code for that iteration.
Example:
for num in range(5):
if num == 2:
continue #skip printing number 2
print(num)
3. break statement
Purpose: exit the loop entirely, regardless of the loop condition.
Effect: The loop ends immediately.
Example
for num in range(5):
if num == 3:
break
print(num)
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