Python Loops

Loops in Python are used to execute a block of code repeatedly based on a condition or for iterating over a sequence. They are essential for performing repetitive tasks efficiently.

1. for Loop

The for loop in Python is used to iterate over a sequence (like a list, tuple, dictionary, set, or string) or other iterable objects.

Basic Syntax:

for variable in sequence:
    # Code block to execute

Example:

Iterating over a List

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

Output:

apple
banana
cherry

Explanation:

• The for loop iterates over each item in the fruits list and prints it.

Iterating over a Range

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

Output:

0
1
2
3
4

Explanation:

• The range(5) generates numbers from 0 to 4, and the loop prints each number.

Iterating over a Dictionary

person = {'name': 'Alice', 'age': 25, 'city': 'New York'}
for key, value in person.items():
    print(key, value)

Output:

name Alice
age 25
city New York

Explanation:

• The items() method returns key-value pairs of the dictionary, which are iterated and printed.

2. while Loop

The while loop in Python continues to execute a block of code as long as a specified condition is True.

Basic Syntax:

while condition:
    # Code block to execute

Example:

Basic while Loop

count = 0
while count < 5:
    print(count)
    count += 1

Output:

0
1
2
3
4

Explanation:

• The loop continues as long as count is less than 5. The count variable is incremented in each iteration.

while Loop with break

count = 0
while True:
    if count >= 5:
        break
    print(count)
    count += 1

Output:

0
1
2
3
4

Explanation:

• The while True loop runs indefinitely but is terminated by the break statement when count reaches 5.

while Loop with continue

count = 0
while count < 5:
    count += 1
    if count % 2 == 0:
        continue
    print(count)

Output:

1
3

Explanation:

• The continue statement skips the rest of the code in the loop for even values of count, so only odd numbers are printed.

3. Nested Loops

Loops can be nested within each other to perform more complex iterations.

Example:

Nested for Loops

for i in range(3):
    for j in range(3):
        print(f"i={i}, j={j}")

Output:

i=0, j=0
i=0, j=1
i=0, j=2
i=1, j=0
i=1, j=1
i=1, j=2
i=2, j=0
i=2, j=1
i=2, j=2

Explanation:

• The outer loop runs 3 times, and for each iteration of the outer loop, the inner loop runs 3 times.

4. Loop Control Statements

4.1. break

The break statement terminates the loop prematurely.

Example:

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

Output:

0
1
2
3
4

Explanation:

• The loop breaks when i equals 5, so only numbers from 0 to 4 are printed.

4.2. continue

The continue statement skips the current iteration and moves to the next iteration.

Example:

for i in range(10):
    if i % 2 == 0:
        continue
    print(i)

Output:

1
3
5
7
9

Explanation:

• Even numbers are skipped due to the continue statement, so only odd numbers are printed.

4.3. pass

The pass statement is a placeholder that does nothing and is used when a statement is syntactically required but no action is needed.

Example:

for i in range(3):
    pass  # No operation performed

Explanation:

• The pass statement does nothing; the loop executes without performing any actions.

Conclusion

Loops in Python are powerful constructs for executing repetitive tasks and iterating over sequences. By understanding the for and while loops, as well as loop control statements like break, continue, and pass, you can write efficient and effective code for various programming tasks.