Python Loops Basics

Loops are one of the most powerful concepts in any programming language.
They allow you to repeat a block of code multiple times — saving effort, avoiding repetition, and making your programs more efficient.

In this guide, you’ll learn everything about Python loops, including:

• for loop
• while loop
• break, continue, and pass statements
• Loop else blocks
• Common examples and use cases

Let’s dive in! 🚀

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🧠 What is a Loop?

A loop allows you to execute a block of code repeatedly until a certain condition is met.

There are mainly two types of loops in Python:

1. for loop – Used for iterating over a sequence (like list, tuple, dictionary, string, or range).
2. while loop – Used for repeating a block of code as long as a condition is True.

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🔹 1. for Loop

The for loop is used when you want to iterate over a sequence (like a list, tuple, or string) and perform actions for each element.

🧩 Syntax:

for variable in sequence:
    # Code block

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✅ Example 1: Looping through a list

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

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✅ Example 2: Looping through a string

for char in "Python":
    print(char)

Output:

P
y
t
h
o
n

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✅ Example 3: Using range() in loops

The range() function generates a sequence of numbers.

for i in range(5):
    print(i)

Output:

0
1
2
3
4

👉 By default, range(start, stop, step) starts at 0 and stops before the given number.

Example with step:

for i in range(2, 10, 2):
    print(i)

Output:

2
4
6
8

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✅ Example 4: Looping through a list using range()

Sometimes, you may want to use indexes while looping through a list — for example, when you need both the index and the value.

fruits = ["apple", "banana", "cherry"]
for i in range(len(fruits)):
    print(f"Index {i}: {fruits[i]}")

Output:

Index 0: apple
Index 1: banana
Index 2: cherry

💡 Tip:
You can also use the built-in enumerate() function for cleaner index-based looping:

for i, fruit in enumerate(fruits):
    print(i, fruit)

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✅ Example 5: Looping through a dictionary

When looping through dictionaries, you can iterate over:

• Keys
• Values
• Key-value pairs

person = {"name": "Alice", "age": 25, "city": "Mumbai"}

# Loop through keys
for key in person:
    print(key)

# Loop through values
for value in person.values():
    print(value)

# Loop through key-value pairs
for key, value in person.items():
    print(f"{key}: {value}")

Output:

name
age
city
Alice
25
Mumbai
name: Alice
age: 25
city: Mumbai

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🔹 2. while Loop

A while loop executes a block of code as long as the condition is True.

🧩 Syntax:

while condition:
    # Code block

✅ Example: Counting numbers

count = 1
while count <= 5:
    print(count)
    count += 1

Output:

1
2
3
4
5

⚠️ If the condition never becomes False, the loop runs forever (infinite loop).

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🔸 3. Loop Control Statements

Python provides three special statements to control the flow of loops:

➤ break

Stops the loop entirely when a certain condition is met.

for i in range(10):
    if i == 5:
        break
    print(i)

Output:

0
1
2
3
4

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➤ continue

Skips the current iteration and moves to the next one.

for i in range(6):
    if i == 3:
        continue
    print(i)

Output:

0
1
2
4
5

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➤ pass

Used as a placeholder when you don’t want to execute any code yet.

for i in range(5):
    pass  # Placeholder for future code

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🔸 4. Loop else Block

An else block can be added to loops in Python.
The else part runs after the loop finishes normally (not when stopped by break).

✅ Example:

for i in range(5):
    print(i)
else:
    print("Loop completed successfully!")

Output:

0
1
2
3
4
Loop completed successfully!

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🔹 5. Nested Loops

You can place one loop inside another loop — useful for working with multi-dimensional data like matrices or nested lists.

for i in range(1, 4):
    for j in range(1, 4):
        print(f"({i}, {j})", end=" ")
    print()

Output:

(1, 1) (1, 2) (1, 3) 
(2, 1) (2, 2) (2, 3) 
(3, 1) (3, 2) (3, 3)

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🧰 6. Common Loop Use Cases

Use Case	Example
Print numbers 1–10	for i in range(1, 11): print(i)
Sum of numbers	sum = 0; for i in range(1,6): sum += i
Loop through dictionary	for k,v in dict.items(): print(k,v)
Search element in list	for item in list: if item==target: break
Filter even numbers	[x for x in range(10) if x%2==0]

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🔍 Bonus: List Comprehensions (Short Loops in One Line)

Python allows loops in a single line to create lists concisely.

squares = [x**2 for x in range(5)]
print(squares)

Output:

[0, 1, 4, 9, 16]

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🧩 Summary Table

Type	Syntax	Use Case
for loop	for i in sequence:	Iterate over sequences (lists, strings, etc.)
while loop	while condition:	Repeat until condition becomes False
break	—	Stop loop early
continue	—	Skip current iteration
pass	—	Placeholder (does nothing)
else	for/while ... else:	Runs when loop finishes normally

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💡 Final Thoughts

Loops are the core building blocks of Python programming.
They make your code more efficient and dynamic by avoiding repetition.

Remember:

• Use for loops for iterating over collections.
• Use while loops for condition-based repetition.
• Use break, continue, and pass to control loop flow.