? For Loops in Python

A for loop in Python is used to iterate over a sequence (like a list, tuple, string, or range) and execute a block of code for each item in the sequence.

Basic Syntax:

for item in sequence:    # Execute this block of code for each item    # Indented code block

? 1. Looping through a List

You can loop through a list and perform operations on each item.

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

• Output:

  applebananacherry

? 2. Looping through a String

You can iterate over each character in a string.

word = "hello"for letter in word:    print(letter)

• Output:

  hello

? 3. Using range() for Loops

The range() function generates a sequence of numbers, which is often used in for loops to repeat actions a specific number of times.

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

• Output:

  01234

• Explanation: range(5) generates numbers from 0 to 4. The loop iterates over each of these numbers.

You can also specify a start and stop value in range().

for i in range(2, 6):    print(i)

• Output:

  2345

You can also define a step size:

for i in range(0, 10, 2):    print(i)

• Output:

  02468

? 4. Nested For Loops

You can use for loops inside other for loops to iterate over multi-dimensional structures like lists of lists.

matrix = [    [1, 2, 3],    [4, 5, 6],    [7, 8, 9]]for row in matrix:    for num in row:        print(num, end=" ")    print()  # Adds a newline after each row

• Output:

  1 2 3 4 5 6 7 8 9 

? 5. Looping through a Dictionary

You can loop through the keys and values of a dictionary.

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

• Output:

  name : Aliceage : 25city : New York

You can also loop through just the keys or just the values:

# Loop through keysfor key in person:    print(key)# Loop through valuesfor value in person.values():    print(value)

? 6. Using else with For Loops

The else block can be used with a for loop, and it will execute when the loop completes normally (i.e., without encountering a break statement).

for i in range(3):    print(i)else:    print("Loop finished.")

• Output:

  012Loop finished.

• Explanation: The else part runs after the loop finishes executing all iterations.

? 7. Break and Continue in For Loops

• break: Stops the loop entirely when a certain condition is met.

for i in range(5):    if i == 3:        break    print(i)

• Output:

  012

• continue: Skips the current iteration and continues with the next one.

for i in range(5):    if i == 3:        continue    print(i)

• Output:

  0124

? 8. For Loop with List Comprehension

A list comprehension is a more compact way to create lists using a for loop. It allows you to iterate over a sequence and return a new list in a single line of code.

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

• Output:

  [0, 1, 4, 9, 16]

List comprehensions can also include conditions:

even_squares = [x**2 for x in range(10) if x % 2 == 0]print(even_squares)

• Output:

  [0, 4, 16, 36, 64]

Summary of For Loop Examples:

• Basic iteration: for item in sequence

• Using range(): for i in range(start, stop, step)

• Nested loops: for item in sequence: for sub_item in sub_sequence

• Looping through a dictionary: for key, value in dictionary.items()

• Using else: The else block runs after the loop finishes (unless a break is encountered).

• break and continue: Control the loop’s flow by either stopping or skipping iterations.

• List comprehensions: Compact syntax to create lists from a sequence.

By using these techniques, you can create efficient and readable loops in Python. Let me know if you need more examples or details! ?