What is the "for" loop in Python and how to use it?

Question

Jayant Kumar · Accepted Answer

Table of Contants
Introduction:
A for loop in Python is a control flow statement that allows you to iterate over a sequence (such as a list, tuple, string, or range) and execute a block of code for each item in that sequence. Unlike a while loop, where the number of iterations depends on a condition, the for loop runs for a fixed number of iterations based on the length of the sequence being looped over.
Basic Syntax of the for Loop
for item in sequence:
    # Code block to execute for each item

**item**: A variable that takes the value of each element in the sequence on each iteration.
**sequence**: The collection (list, tuple, string, etc.) that the loop iterates over.

Example: Basic for Loop
fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)

The loop iterates over each element in the fruits list, printing each fruit: "apple," "banana," and "cherry."

How the for Loop Works

The loop picks the first item from the sequence and assigns it to the item variable.
It executes the code block for the current item.
After the block is executed, the next item in the sequence is assigned to item, and the process repeats.
The loop ends when there are no more items in the sequence.

Practical Use Cases for the for Loop

Looping Over a List or Tuple:

You can use the for loop to iterate over the elements of a list, tuple, or any other collection.
Example:
numbers = [1, 2, 3, 4, 5]

for num in numbers:
    print(num)

The loop prints each number in the list.

Looping Over a String:

The for loop can be used to iterate over each character in a string.
Example:
word = "Python"

for char in word:
    print(char)

The loop prints each character of the string "Python" on a new line.

Looping Over a Dictionary:

You can use the for loop to iterate over the keys and values in a dictionary.
Example:
student_grades = {"Alice": 85, "Bob": 90, "Charlie": 78}

for name, grade in student_grades.items():
    print(f"{name}: {grade}")

The loop prints the names and grades of the students.

The range() Function with a for Loop
The range() function generates a sequence of numbers, making it easy to loop over a specific range of values.
Example:
for i in range(5):
    print(i)

The loop prints numbers from 0 to 4. The range(5) function generates numbers starting from 0 up to (but not including) 5.

Example: Specifying Start and Step in range()
for i in range(2, 10, 2):
    print(i)

This loop prints even numbers between 2 and 10 (not inclusive). The range(2, 10, 2) function specifies a start of 2, an end of 10, and a step of 2.

Controlling the for Loop with break and continue
1. **break** Statement:
The break statement terminates the loop immediately, regardless of whether all items have been iterated over.
Example: Exiting the Loop with break
for num in range(10):
    if num == 5:
        break
    print(num)

The loop prints numbers from 0 to 4 and then stops when num equals 5 due to the break statement.

2. **continue** Statement:
The continue statement skips the current iteration and moves on to the next one.
Example: Skipping an Iteration with continue
for num in range(5):
    if num == 3:
        continue
    print(num)

The loop skips printing the number 3 and continues with the next iteration.

Using the else Clause with a for Loop
Python allows an else clause to be used with a for loop. The else block is executed after the loop completes all its iterations unless the loop is terminated with a break.
Example:
for num in range(5):
    print(num)
else:
    print("Loop finished.")

The else block runs after the loop has printed all numbers from 0 to 4, printing "Loop finished."

Practical Examples of Using the for Loop
1. Summing Numbers in a List:
You can use the for loop to sum the values in a list.
numbers = [1, 2, 3, 4, 5]
total = 0

for num in numbers:
    total += num
print(f"Total sum: {total}")

The loop adds each number in the list to the total, which ends up as 15.

2. Finding Even Numbers:
The for loop can be used to find and print even numbers in a range.
for num in range(1, 11):
    if num % 2 == 0:
        print(f"{num} is even.")

This loop checks if each number in the range 1 to 10 is divisible by 2 and prints the even numbers.

3. Nested **for** Loops:
You can nest for loops to iterate over multiple dimensions, such as in a matrix or a list of lists.
matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

for row in matrix:
    for item in row:
        print(item, end=" ")
    print()

The outer loop iterates over rows, and the inner loop iterates over items in each row, printing a 3x3 matrix.

Conclusion:
The for loop in Python is a versatile control structure that allows you to iterate over sequences like lists, tuples, and strings. It is useful for situations where you need to perform repetitive tasks or process items in a sequence. Combined with features like the range() function, break, and continue statements, the for loop becomes a powerful tool for efficiently handling iterations in your Python programs.

What is the "for" loop in Python and how to use it?

Table of Contants

Introduction:

Basic Syntax of the `for` Loop

Example: Basic `for` Loop

How the `for` Loop Works

Practical Use Cases for the `for` Loop

Example:

Example:

Example:

The `range()` Function with a `for` Loop

Example:

Example: Specifying Start and Step in `range()`

Controlling the `for` Loop with `break` and `continue`

1. `break` Statement:

Example: Exiting the Loop with `break`

2. `continue` Statement:

Example: Skipping an Iteration with `continue`

Using the `else` Clause with a `for` Loop

Example:

Practical Examples of Using the `for` Loop

1. Summing Numbers in a List:

2. Finding Even Numbers:

3. Nested `for` Loops:

Conclusion:

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